Use the CC_CHECK_FLAGS_APPEND() m4 macro to test for availability of
CFLAGS and LFLAGS. It automatically drops the unavailable flags.
This is also used by systemd, so it ought to work with ostree and other
non-standard build-environments.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
