[PATCH bpf-next] bpf: handle implicit declaration of function gettid in bpf_iter.c

[Jason Xing <kerneljasonxing@xxxxxxxxx>]

From: Jason Xing <kernelxing@xxxxxxxxxxx>

As we can see from the title, when I compiled the selftests/bpf, I
saw the error:
implicit declaration of function ‘gettid’ ; did you mean ‘getgid’? [-Werror=implicit-function-declaration]
  skel->bss->tid = gettid();
                   ^~~~~~
                   getgid

Adding a define to fix it (referring to
tools/perf/tests/shell/coresight/thread_loop/thread_loop.c file.

Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/bpf_iter.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index f0a3a9c18e9e..a105759f3dcf 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -34,6 +34,8 @@
 #include "bpf_iter_ksym.skel.h"
 #include "bpf_iter_sockmap.skel.h"
 
+#define gettid() syscall(SYS_gettid)
+
 static void test_btf_id_or_null(void)
 {
 	struct bpf_iter_test_kern3 *skel;
-- 
2.37.3