xf86atomic: require CAS support in libatomic_ops

Since AO_compare_and_swap_full() is used by libdrm, AO_REQUIRE_CAS must be defined before including <atomic_ops.h> so that we are sure that CAS support will be provided. This is necessary to make sure that the AO_compare_and_swap_full() function will be provided on all architectures, including the ones that don't have built-in CAS support such as SPARCv8.

Signed-off-by: Thomas Petazzoni thomas.petazzoni@free-electrons.com Signed-off-by: Peter Seiderer ps.report@gmx.net