Set -fsanitize=undefined on CI.

Propagate CXXFLAGS correctly.
Set CFLAGS in the same way.

Author: redboltz

.github/workflows/gha.yml

@@ -61,7 +61,7 @@ jobs:
         cd ..
 
         # build and test
-        CMAKE_CXX_COMPILER="${CXX}" CMAKE_C_COMPILER="${CC}" GTEST_ROOT="${BASE}/usr" CFLAGS="-Werror -g" CXXFLAGS="-Werror -g" ${ACTION}
+        CMAKE_CXX_COMPILER="${CXX}" CMAKE_C_COMPILER="${CC}" GTEST_ROOT="${BASE}/usr" CFLAGS="-Werror -g -fsanitize=undefined" CXXFLAGS="-Werror -g -fsanitize=undefined" ${ACTION}
 
   linux:
     runs-on: ubuntu-18.04
@@ -172,7 +172,7 @@ jobs:
         fi
 
         # build and test
-        CMAKE_CXX_COMPILER="${CXX}" CMAKE_C_COMPILER="${CC}" GTEST_ROOT="${BASE}/usr" CFLAGS="-Werror -g" CXXFLAGS="-Werror -g" MSGPACK_SAN="${SAN}" ${ACTION}
+        CMAKE_CXX_COMPILER="${CXX}" CMAKE_C_COMPILER="${CC}" GTEST_ROOT="${BASE}/usr" CFLAGS="-Werror -g -fsanitize=undefined" CXXFLAGS="-Werror -g -fsanitize=undefined" MSGPACK_SAN="${SAN}" ${ACTION}
 
   windows:
     runs-on: windows-2019

ci/build_cmake.sh

@@ -25,7 +25,7 @@ else
     export ARCH_FLAG="-m64"
 fi
 
-cmake -DMSGPACK_32BIT=${BIT32} -DBUILD_SHARED_LIBS=${SHARED} -DMSGPACK_CHAR_SIGN=${CHAR_SIGN} -DCMAKE_CXX_FLAGS=${ARCH_FLAG} ..
+cmake -DMSGPACK_32BIT=${BIT32} -DBUILD_SHARED_LIBS=${SHARED} -DMSGPACK_CHAR_SIGN=${CHAR_SIGN} -DCMAKE_CXX_FLAGS="${ARCH_FLAG} ${CXXFLAGS}" -DCMAKE_C_FLAGS="${CFLAGS}" ..
 
 ret=$?
 if [ $ret -ne 0 ]