perf tools: Fix build errors with mipsel-linux-uclibc compiler

linux/tools$ make ARCH=mips CROSS_COMPILE=mipsel-linux- perf
...
config/Makefile:256: *** No gnu/libc-version.h found, please install
glibc-dev[el].  Stop.
make[1]: *** [all] Error 2
make: *** [perf] Error 2

...
In file included from builtin-sched.c:13:0:
util/cloexec.h:8:12: error: redundant redeclaration of ‘sched_getcpu’
 [-Werror=redundant-decls]
 extern int sched_getcpu(void) __THROW;

mipsel-buildroot-linux-uclibc/sysroot/usr/include/bits/sched.h:88:12:
 note: previous declaration of ‘sched_getcpu’ was here
 extern int sched_getcpu (void) __THROW;

uclibc info:
sysroot/usr/include/bits/uClibc_config.h
__UCLIBC_MAJOR__ 0
__UCLIBC_MINOR__ 9
__UCLIBC_SUBLEVEL__ 33

sysroot/usr/include/features.h
__UCLIBC__ 1
__GLIBC__ 2
__GLIBC_MINOR__ 2

Signed-off-by: Petri Gynther <pgynther@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1438735081-24131-1-git-send-email-pgynther@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>