perf tools: Define _GNU_SOURCE on pthread_attr_setaffinity_np feature check
perf tools: Define _GNU_SOURCE on pthread_attr_setaffinity_np feature check

The man page for pthread_attr_set_affinity_np states that _GNU_SOURCE
must be defined before pthread.h is included in order to get the proper
function declaration.  Define this in the Makefile.

Without this defined, the feature check fails on a Fedora system with
gcc5 and then the perf build later fails with conflicting prototypes for
the function.

Signed-off-by: Josh Boyer <94755a79aca753e683bb6d0e796d473b797056eb@fedoraproject.org>
Cc: Jiri Olsa <2c6594f608aa3d41e98d48846a6328831f7084ad@kernel.org>
Cc: Peter Zijlstra <645ca7d3a8d3d4f60557176cd361ea8351edc32b@chello.nl>
Cc: Vineet Gupta <bd05ca6cff4fa9f3083b4f5f4cfd92a96f3c3adb@synopsys.com>
Link: 7ed80a28b223d20e809824168a7ec4f95cfb89c7@hansolo.redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <293abb6b76d7791c0732cc517d38c4b5c734b87f@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs