[PATCH bpf-next v1 14/19] selftests/bpf: Fix compiling tcp_rtt.c with musl-libc

[Tony Ambardar <tony.ambardar@xxxxxxxxx>]

The GNU version of 'struct tcp_info' in 'netinet/tcp.h' is not exposed by
musl headers unless _GNU_SOURCE is defined.

Add this definition to fix errors seen compiling for mips64el/musl-libc:

  tcp_rtt.c: In function 'wait_for_ack':
  tcp_rtt.c:24:25: error: storage size of 'info' isn't known
     24 |         struct tcp_info info;
        |                         ^~~~
  tcp_rtt.c:24:25: error: unused variable 'info' [-Werror=unused-variable]
  cc1: all warnings being treated as errors

Fixes: 1f4f80fed217 ("selftests/bpf: test_progs: convert test_tcp_rtt")
Signed-off-by: Tony Ambardar <tony.ambardar@xxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/tcp_rtt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c b/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c
index f2b99d95d916..c38784c1c066 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c
@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
 #include <test_progs.h>
 #include "cgroup_helpers.h"
 #include "network_helpers.h"
-- 
2.34.1