Allow using other compilers such as clang. Without this, the build fails
when $(CFLAGS) contains clang-specific flags:
gcc: error: unrecognized command line option '-Weverything'
Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
libsemanage/tests/Makefile currently overwrites CFLAGS and LDFLAGS
contents. This makes building with custom flags (e.g. with address
sanitizer) harder. Append flags to these variables instead.
Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>