selftests/bpf: test_progs: test__skip

Export test__skip() to indicate skipped tests and use it in
test_send_signal_nmi().

Cc: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/prog_tests/send_signal.c

@@ -204,6 +204,7 @@ static int test_send_signal_nmi(void)
 		if (errno == ENOENT) {
 			printf("%s:SKIP:no PERF_COUNT_HW_CPU_CYCLES\n",
 			       __func__);
+			test__skip();
 			return 0;
 		}
 		/* Let the test fail with a more informative message */