perf bench numa: Share sched_getcpu() __weak def with cloexec.c

perf bench numa: Share sched_getcpu() __weak def with cloexec.c

We really should move the sched_getcpu() to some more suitable place,
but this one-liner fixes this build problem on ancient distros like
RHEL5.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vinson Lee <vlee@twitter.com>
Link: http://lkml.kernel.org/n/tip-5yqg4p11f9uii6yremz3r35v@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>