[PATCH bpf-next] libbpf: add _GNU_SOURCE for reallocarray to ringbuf.c

[Andrii Nakryiko <andriin@xxxxxx>]

On systems with recent enough glibc, reallocarray compat won't kick in, so
reallocarray() itself has to come from stdlib.h include. But _GNU_SOURCE is
necessary to enable it. So add it.

Fixes: 4cff2ba58bf1 ("libbpf: Add BPF ring buffer support")
Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
---
 tools/lib/bpf/ringbuf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/lib/bpf/ringbuf.c b/tools/lib/bpf/ringbuf.c
index bc10fa1d43c7..4fc6c6cbb4eb 100644
--- a/tools/lib/bpf/ringbuf.c
+++ b/tools/lib/bpf/ringbuf.c
@@ -4,6 +4,9 @@
  *
  * Copyright (C) 2020 Facebook, Inc.
  */
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
 #include <stdlib.h>
 #include <stdio.h>
 #include <errno.h>
-- 
2.24.1