perf bench numa: Fix to show proper convergence stats

With commit: e1e455f (perf tools: Work around lack of sched_getcpu
in glibc < 2.6), perf_bench numa mem with -c or -m option is not able to
correctly calculate convergence.

With the above commit, sched_getcpu always seems to return -1. The
intention of commit e1e455f was to add a sched_getcpu in glibc < 2.6.
Hence keep the sched_getcpu definition under an ifdef.

This regression happened occurred between v4.0 and v4.1

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Vinson Lee <vlee@twitter.com>
Fixes:  e1e455f ("perf tools: Work around lack of sched_getcpu in glibc < 2.6")
Link: http://lkml.kernel.org/r/20150624111004.GA5220@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/cloexec.c

@@ -7,11 +7,15 @@
 
 static unsigned long flag = PERF_FLAG_FD_CLOEXEC;
 
+#ifdef __GLIBC_PREREQ
+#if !__GLIBC_PREREQ(2, 6)
 int __weak sched_getcpu(void)
 {
 	errno = ENOSYS;
 	return -1;
 }
+#endif
+#endif
 
 static int perf_flag_probe(void)
 {