tools build feature sched_getcpu: Undef _GNU_SOURCE at the end

mainline inclusion
from mainline-5.0
commit 44ec8396e2da
category: bugfix
bugzilla: 11720
CVE: NA

-------------------------------------------------

Since this feature test is included in test-all.c, the feature detection
fast path compile/link phase, it can't leave any defines behind, as it
can affect the tests included after it, so remove it.
Reported-by: NJiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lkml.kernel.org/n/tip-lg3kpd9tzypc797vb1f42u6k@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>
Reviewed-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

tools/build/feature/test-sched_getcpu.c

@@ -8,3 +8,5 @@ int main(void)
 {
 	return sched_getcpu();
 }
+
+#undef _GNU_SOURCE