selftests/bpf: Make sure enum-less bpf_enable_stats() API works in C++ mode

Just a simple test to make sure we don't introduce unwanted compiler
warnings and API still supports passing enums as input argument.

Signed-off-by: Andrii Nakryiko <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/test_cpp.cpp

···
 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
 #include <iostream>
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+#include <unistd.h>
+#include <linux/bpf.h>
+#include <linux/btf.h>
 #include <bpf/libbpf.h>
-#pragma GCC diagnostic pop
 #include <bpf/bpf.h>
 #include <bpf/btf.h>
 #include "test_core_extern.skel.h"
···
 	struct btf_dump_opts opts = { };
 	struct test_core_extern *skel;
 	struct btf *btf;
+	int fd;
 
 	try_skeleton_template();
 
···
 	/* BPF skeleton */
 	skel = test_core_extern__open_and_load();
 	test_core_extern__destroy(skel);
+
+	fd = bpf_enable_stats(BPF_STATS_RUN_TIME);
+	if (fd < 0)
+		std::cout << "FAILED to enable stats: " << fd << std::endl;
+	else
+		::close(fd);
 
 	std::cout << "DONE!" << std::endl;