CI: Introduce and use LIBPCAP_CMAKE_TAINTED

The new environment variable provides means to declare all or some libpcap
cmake run of a specific environment (CI or a working copy) as tainted.
Add explicit conditions to exempt the cmake run that emit warnings
now and request the compiler to treat warnings as errors *iff* the cmake
run is not tainted. This way if a cmake run that is warning-free now
degrades later, CI will fail it.

The treat warnings as errors cmake option used is:
-Werror=dev
       Make developer warnings errors.

       Make  warnings  that  are  meant  for  the  author of the CMake-
       Lists.txt files errors. By default this will also turn on depre-
       cated warnings as errors.

1 files changed, 7 insertions, 0 deletions

diff --git a/build_matrix.sh b/build_matrix.sh
index 60065966..01ac3205 100755
--- a/build_matrix.sh
+++ b/build_matrix.sh
@@ -6,6 +6,12 @@
 : "${MATRIX_CC:=gcc clang}"
 : "${MATRIX_CMAKE:=no yes}"
 : "${MATRIX_REMOTE:=no yes}"
+# Set this variable to "yes" before calling this script to disregard all cmake
+# warnings in a particular environment (CI or a local working copy).  Set it
+# to "yes" in this script or in build.sh when a matrix subset is known to be
+# not cmake warning-free because of the version or whatever other factor
+# that the scripts can detect both in and out of CI.
+: "${LIBPCAP_CMAKE_TAINTED:=no}"
 # Set this variable to "yes" before calling this script to disregard all
 # warnings in a particular environment (CI or a local working copy).  Set it
 # to "yes" in this script or in build.sh when a matrix subset is known to be
@@ -28,6 +34,7 @@ if [ -z "$PREFIX" ]; then
 fi
 COUNT=0
 export LIBPCAP_TAINTED
+export LIBPCAP_CMAKE_TAINTED
 if command -v valgrind >/dev/null 2>&1; then
     VALGRIND_CMD="valgrind --leak-check=full --error-exitcode=1"
     export VALGRIND_CMD