rt-tests Makefile: separate CFLAGS and CPPFLAGS

For compilation to work

        -D_GNU_SOURCE -Isrc/include

is needed to be passed to the compiler. For Debian packaging several
things are added but not these two from above. So be a bit more friendly
and add them unconditionally. There is no harm if they are included in
the user supplied CFLAGS and so passed twice.

Moreover be a bit more correct about CFLAGS/CPPFLAGS. Both should be
passed to the compiler with CFLAGS taking options for the compiler and
CPPFLAGS taking options for the preprocessor. This is also needed for
Debian packaging where the helper scripts set CPPFLAGS.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: John Kacur <jkacur@redhat.com>
1 file changed