configure: use ac_c_werror_flag to force unknown compiler flags to fail.

It's not a documented feature, but it's what the documented
AC_LANG_WERROR has used for 13 years, and there's no push/pop mechanism
for AC_LANG_WERROR, so you can't ensure that "fail even on warnings"
will be applied *only* in AC_LBL_CHECK_COMPILER_OPT(), as that's what we
want.  (If we can make sure that *no* compiler tests will produce
warnings, except for the ones we *want* to fail if they produce
warnings, we could just do AC_LANG_WERROR, but that might be tricky to
ensure in the general case.)

We do this because not all compilers have a command-line flag to force
all warnings, *including* warnings from unknown commad-line flags (I'm
looking at *you* IBM XL C!), so we have to have the test check to make
sure no warnings are produced (which, for AC_TRY_COMPILE(), means
"nothing is written to the standard output").

2 files changed, 273 insertions, 319 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index 2fd29fed..18858536 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -232,36 +232,6 @@ AC_DEFUN(AC_LBL_C_INIT,
 ])
 
 dnl
-dnl Check whether, if you pass an unknown warning option to the
-dnl compiler, it fails or just prints a warning message and succeeds.
-dnl Set ac_lbl_unknown_warning_option_error to the appropriate flag
-dnl to force an error if it would otherwise just print a warning message
-dnl and succeed.
-dnl
-AC_DEFUN(AC_LBL_CHECK_UNKNOWN_WARNING_OPTION_ERROR,
-    [
-	AC_MSG_CHECKING([whether the compiler fails when given an unknown warning option])
-	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS -Wxyzzy-this-will-never-succeed-xyzzy"
-	AC_TRY_COMPILE(
-	    [],
-	    [return 0],
-	    [
-		AC_MSG_RESULT([no])
-		#
-		# We're assuming this is clang, where
-		# -Werror=unknown-warning-option is the appropriate
-		# option to force the compiler to fail.
-		#
-		ac_lbl_unknown_warning_option_error="-Werror=unknown-warning-option"
-	    ],
-	    [
-		AC_MSG_RESULT([yes])
-	    ])
-	CFLAGS="$save_CFLAGS"
-    ])
-
-dnl
 dnl Check whether the compiler option specified as the second argument
 dnl is supported by the compiler and, if so, add it to the macro
 dnl specified as the first argument
@@ -278,18 +248,18 @@ AC_DEFUN(AC_LBL_CHECK_COMPILER_OPT,
     [
 	AC_MSG_CHECKING([whether the compiler supports the $2 option])
 	save_CFLAGS="$CFLAGS"
-	if expr "x$2" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error $2"
-	elif expr "x$2" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror $2"
-	elif expr "x$2" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror $2"
-	else
-	    CFLAGS="$CFLAGS $2"
-	fi
+	CFLAGS="$CFLAGS $2"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	AC_TRY_COMPILE(
 	    [],
 	    [return 0],
@@ -332,6 +302,7 @@ AC_DEFUN(AC_LBL_CHECK_COMPILER_OPT,
 		AC_MSG_RESULT([no])
 		CFLAGS="$save_CFLAGS"
 	    ])
+	ac_c_werror_flag="$save_ac_c_werror_flag"
     ])
 
 dnl
@@ -819,7 +790,6 @@ AC_DEFUN(AC_LBL_DEVEL,
 	    # Skip all the warning option stuff on some compilers.
 	    #
 	    if test "$ac_lbl_cc_dont_try_gcc_dashW" != yes; then
-		    AC_LBL_CHECK_UNKNOWN_WARNING_OPTION_ERROR()
 		    AC_LBL_CHECK_COMPILER_OPT($1, -W)
 		    AC_LBL_CHECK_COMPILER_OPT($1, -Wall)
 		    AC_LBL_CHECK_COMPILER_OPT($1, -Wcomma)
diff --git a/configure b/configure
index 32e6f680..9533523c 100755
--- a/configure
+++ b/configure
@@ -3855,18 +3855,18 @@ esac
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -fvisibility=hidden option" >&5
 $as_echo_n "checking whether the compiler supports the -fvisibility=hidden option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-fvisibility=hidden" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -fvisibility=hidden"
-	elif expr "x-fvisibility=hidden" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -fvisibility=hidden"
-	elif expr "x-fvisibility=hidden" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -fvisibility=hidden"
-	else
-	    CFLAGS="$CFLAGS -fvisibility=hidden"
-	fi
+	CFLAGS="$CFLAGS -fvisibility=hidden"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -3932,6 +3932,7 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
     else
 	    V_INCLS="$V_INCLS -I/usr/local/include"
@@ -3955,18 +3956,18 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -fvisibility=hidden option" >&5
 $as_echo_n "checking whether the compiler supports the -fvisibility=hidden option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-fvisibility=hidden" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -fvisibility=hidden"
-	elif expr "x-fvisibility=hidden" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -fvisibility=hidden"
-	elif expr "x-fvisibility=hidden" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -fvisibility=hidden"
-	else
-	    CFLAGS="$CFLAGS -fvisibility=hidden"
-	fi
+	CFLAGS="$CFLAGS -fvisibility=hidden"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -4032,6 +4033,7 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 		    ;;
 
@@ -4117,18 +4119,18 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -xldscope=hidden option" >&5
 $as_echo_n "checking whether the compiler supports the -xldscope=hidden option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-xldscope=hidden" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -xldscope=hidden"
-	elif expr "x-xldscope=hidden" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -xldscope=hidden"
-	elif expr "x-xldscope=hidden" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -xldscope=hidden"
-	else
-	    CFLAGS="$CFLAGS -xldscope=hidden"
-	fi
+	CFLAGS="$CFLAGS -xldscope=hidden"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -4194,6 +4196,7 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 		    ;;
 
@@ -9368,57 +9371,21 @@ rm -f os-proto.h
 	    #
 	    if test "$ac_lbl_cc_dont_try_gcc_dashW" != yes; then
 
-	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler fails when given an unknown warning option" >&5
-$as_echo_n "checking whether the compiler fails when given an unknown warning option... " >&6; }
-	save_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS -Wxyzzy-this-will-never-succeed-xyzzy"
-	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-
-int
-main ()
-{
-return 0
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-
-		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
-		#
-		# We're assuming this is clang, where
-		# -Werror=unknown-warning-option is the appropriate
-		# option to force the compiler to fail.
-		#
-		ac_lbl_unknown_warning_option_error="-Werror=unknown-warning-option"
-
-else
-
-		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-	CFLAGS="$save_CFLAGS"
-
-
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -W option" >&5
 $as_echo_n "checking whether the compiler supports the -W option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-W" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -W"
-	elif expr "x-W" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -W"
-	elif expr "x-W" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -W"
-	else
-	    CFLAGS="$CFLAGS -W"
-	fi
+	CFLAGS="$CFLAGS -W"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9484,23 +9451,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wall option" >&5
 $as_echo_n "checking whether the compiler supports the -Wall option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wall" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wall"
-	elif expr "x-Wall" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wall"
-	elif expr "x-Wall" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wall"
-	else
-	    CFLAGS="$CFLAGS -Wall"
-	fi
+	CFLAGS="$CFLAGS -Wall"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9566,23 +9534,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wcomma option" >&5
 $as_echo_n "checking whether the compiler supports the -Wcomma option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wcomma" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wcomma"
-	elif expr "x-Wcomma" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wcomma"
-	elif expr "x-Wcomma" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wcomma"
-	else
-	    CFLAGS="$CFLAGS -Wcomma"
-	fi
+	CFLAGS="$CFLAGS -Wcomma"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9648,23 +9617,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wdocumentation option" >&5
 $as_echo_n "checking whether the compiler supports the -Wdocumentation option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wdocumentation" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wdocumentation"
-	elif expr "x-Wdocumentation" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wdocumentation"
-	elif expr "x-Wdocumentation" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wdocumentation"
-	else
-	    CFLAGS="$CFLAGS -Wdocumentation"
-	fi
+	CFLAGS="$CFLAGS -Wdocumentation"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9730,23 +9700,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wformat-nonliteral option" >&5
 $as_echo_n "checking whether the compiler supports the -Wformat-nonliteral option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wformat-nonliteral" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wformat-nonliteral"
-	elif expr "x-Wformat-nonliteral" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wformat-nonliteral"
-	elif expr "x-Wformat-nonliteral" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wformat-nonliteral"
-	else
-	    CFLAGS="$CFLAGS -Wformat-nonliteral"
-	fi
+	CFLAGS="$CFLAGS -Wformat-nonliteral"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9812,23 +9783,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wmissing-noreturn option" >&5
 $as_echo_n "checking whether the compiler supports the -Wmissing-noreturn option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wmissing-noreturn" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wmissing-noreturn"
-	elif expr "x-Wmissing-noreturn" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wmissing-noreturn"
-	elif expr "x-Wmissing-noreturn" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wmissing-noreturn"
-	else
-	    CFLAGS="$CFLAGS -Wmissing-noreturn"
-	fi
+	CFLAGS="$CFLAGS -Wmissing-noreturn"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9894,23 +9866,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wmissing-prototypes option" >&5
 $as_echo_n "checking whether the compiler supports the -Wmissing-prototypes option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wmissing-prototypes" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wmissing-prototypes"
-	elif expr "x-Wmissing-prototypes" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wmissing-prototypes"
-	elif expr "x-Wmissing-prototypes" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wmissing-prototypes"
-	else
-	    CFLAGS="$CFLAGS -Wmissing-prototypes"
-	fi
+	CFLAGS="$CFLAGS -Wmissing-prototypes"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -9976,23 +9949,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wmissing-variable-declarations option" >&5
 $as_echo_n "checking whether the compiler supports the -Wmissing-variable-declarations option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wmissing-variable-declarations" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wmissing-variable-declarations"
-	elif expr "x-Wmissing-variable-declarations" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wmissing-variable-declarations"
-	elif expr "x-Wmissing-variable-declarations" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wmissing-variable-declarations"
-	else
-	    CFLAGS="$CFLAGS -Wmissing-variable-declarations"
-	fi
+	CFLAGS="$CFLAGS -Wmissing-variable-declarations"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10058,23 +10032,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wpointer-arith option" >&5
 $as_echo_n "checking whether the compiler supports the -Wpointer-arith option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wpointer-arith" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wpointer-arith"
-	elif expr "x-Wpointer-arith" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wpointer-arith"
-	elif expr "x-Wpointer-arith" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wpointer-arith"
-	else
-	    CFLAGS="$CFLAGS -Wpointer-arith"
-	fi
+	CFLAGS="$CFLAGS -Wpointer-arith"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10140,23 +10115,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wpointer-sign option" >&5
 $as_echo_n "checking whether the compiler supports the -Wpointer-sign option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wpointer-sign" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wpointer-sign"
-	elif expr "x-Wpointer-sign" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wpointer-sign"
-	elif expr "x-Wpointer-sign" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wpointer-sign"
-	else
-	    CFLAGS="$CFLAGS -Wpointer-sign"
-	fi
+	CFLAGS="$CFLAGS -Wpointer-sign"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10222,23 +10198,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wshadow option" >&5
 $as_echo_n "checking whether the compiler supports the -Wshadow option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wshadow" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wshadow"
-	elif expr "x-Wshadow" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wshadow"
-	elif expr "x-Wshadow" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wshadow"
-	else
-	    CFLAGS="$CFLAGS -Wshadow"
-	fi
+	CFLAGS="$CFLAGS -Wshadow"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10304,23 +10281,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wsign-compare option" >&5
 $as_echo_n "checking whether the compiler supports the -Wsign-compare option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wsign-compare" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wsign-compare"
-	elif expr "x-Wsign-compare" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wsign-compare"
-	elif expr "x-Wsign-compare" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wsign-compare"
-	else
-	    CFLAGS="$CFLAGS -Wsign-compare"
-	fi
+	CFLAGS="$CFLAGS -Wsign-compare"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10386,23 +10364,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wstrict-prototypes option" >&5
 $as_echo_n "checking whether the compiler supports the -Wstrict-prototypes option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wstrict-prototypes" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wstrict-prototypes"
-	elif expr "x-Wstrict-prototypes" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wstrict-prototypes"
-	elif expr "x-Wstrict-prototypes" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wstrict-prototypes"
-	else
-	    CFLAGS="$CFLAGS -Wstrict-prototypes"
-	fi
+	CFLAGS="$CFLAGS -Wstrict-prototypes"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10468,23 +10447,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wunused-parameter option" >&5
 $as_echo_n "checking whether the compiler supports the -Wunused-parameter option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wunused-parameter" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wunused-parameter"
-	elif expr "x-Wunused-parameter" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wunused-parameter"
-	elif expr "x-Wunused-parameter" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wunused-parameter"
-	else
-	    CFLAGS="$CFLAGS -Wunused-parameter"
-	fi
+	CFLAGS="$CFLAGS -Wunused-parameter"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10550,23 +10530,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wused-but-marked-unused option" >&5
 $as_echo_n "checking whether the compiler supports the -Wused-but-marked-unused option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wused-but-marked-unused" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wused-but-marked-unused"
-	elif expr "x-Wused-but-marked-unused" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wused-but-marked-unused"
-	elif expr "x-Wused-but-marked-unused" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wused-but-marked-unused"
-	else
-	    CFLAGS="$CFLAGS -Wused-but-marked-unused"
-	fi
+	CFLAGS="$CFLAGS -Wused-but-marked-unused"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10632,6 +10613,7 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 		    # Warns about safeguards added in case the enums are
 		    # extended
@@ -10664,18 +10646,18 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wunreachable-code option" >&5
 $as_echo_n "checking whether the compiler supports the -Wunreachable-code option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wunreachable-code" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wunreachable-code"
-	elif expr "x-Wunreachable-code" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wunreachable-code"
-	elif expr "x-Wunreachable-code" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wunreachable-code"
-	else
-	    CFLAGS="$CFLAGS -Wunreachable-code"
-	fi
+	CFLAGS="$CFLAGS -Wunreachable-code"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10748,23 +10730,24 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 
 	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether the compiler supports the -Wshorten-64-to-32 option" >&5
 $as_echo_n "checking whether the compiler supports the -Wshorten-64-to-32 option... " >&6; }
 	save_CFLAGS="$CFLAGS"
-	if expr "x-Wshorten-64-to-32" : "x-W.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS $ac_lbl_unknown_warning_option_error -Wshorten-64-to-32"
-	elif expr "x-Wshorten-64-to-32" : "x-f.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wshorten-64-to-32"
-	elif expr "x-Wshorten-64-to-32" : "x-m.*" >/dev/null
-	then
-	    CFLAGS="$CFLAGS -Werror -Wshorten-64-to-32"
-	else
-	    CFLAGS="$CFLAGS -Wshorten-64-to-32"
-	fi
+	CFLAGS="$CFLAGS -Wshorten-64-to-32"
+	#
+	# XXX - yes, this depends on the way AC_LANG_WERROR works,
+	# but no mechanism is provided to turn AC_LANG_WERROR on
+	# *and then turn it back off*, so that we *only* do it when
+	# testing compiler options - 15 years after somebody asked
+	# for it:
+	#
+	#     https://autoconf.gnu.narkive.com/gTAVmfKD/how-to-cancel-flags-set-by-ac-lang-werror
+	#
+	save_ac_c_werror_flag="$ac_c_werror_flag"
+	ac_c_werror_flag=yes
 	cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -10830,6 +10813,7 @@ $as_echo "no" >&6; }
 
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+	ac_c_werror_flag="$save_ac_c_werror_flag"
 
 	    fi