Comment 0 for bug 1871613

Test failed to build with error message below:
make[1]: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf'
make: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests'
stderr:
Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' differs from latest version at 'include/uapi/linux/if_link.h'
prog_tests/send_signal.c: In function 'test_send_signal_common':
prog_tests/send_signal.c:52:3: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
   52 | write(pipe_c2p[1], buf, 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:55:3: warning: ignoring return value of 'read', declared with attribute warn_unused_result [-Wunused-result]
   55 | read(pipe_p2c[0], buf, 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:61:4: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
   61 | write(pipe_c2p[1], "2", 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:63:4: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
   63 | write(pipe_c2p[1], "0", 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:66:3: warning: ignoring return value of 'read', declared with attribute warn_unused_result [-Wunused-result]
   66 | read(pipe_p2c[0], buf, 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:109:2: warning: ignoring return value of 'read', declared with attribute warn_unused_result [-Wunused-result]
  109 | read(pipe_c2p[0], buf, 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:117:2: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
  117 | write(pipe_p2c[1], buf, 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/send_signal.c:131:2: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
  131 | write(pipe_p2c[1], buf, 1);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~
prog_tests/sockmap_basic.c: In function 'connected_socket_v4':
prog_tests/sockmap_basic.c:22:6: warning: implicit declaration of function 'CHECK_FAIL' [-Wimplicit-function-declaration]
   22 | if (CHECK_FAIL(s == -1))
      | ^~~~~~~~~~
prog_tests/sockmap_basic.c:26:22: error: 'SOL_TCP' undeclared (first use in this function); did you mean 'SOL_TIPC'?
   26 | err = setsockopt(s, SOL_TCP, TCP_REPAIR, &repair, sizeof(repair));
      | ^~~~~~~
      | SOL_TIPC
prog_tests/sockmap_basic.c:26:22: note: each undeclared identifier is reported only once for each function it appears in
prog_tests/sockmap_basic.c: In function 'test_sockmap_basic':
prog_tests/sockmap_basic.c:75:6: warning: implicit declaration of function 'test__start_subtest' [-Wimplicit-function-declaration]
   75 | if (test__start_subtest("sockmap create_update_free"))
      | ^~~~~~~~~~~~~~~~~~~
prog_tests/stacktrace_build_id_nmi.c: In function 'read_perf_max_sample_freq':
prog_tests/stacktrace_build_id_nmi.c:12:2: warning: ignoring return value of 'fscanf', declared with attribute warn_unused_result [-Wunused-result]
   12 | fscanf(f, "%llu", &sample_freq);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
make[1]: *** [../lib.mk:141: /home/ubuntu/autotest/client/tmp/ubuntu_bpf/src/linux/tools/testing/selftests/bpf/test_progs] Error 1
make: *** [Makefile:136: all] Error 2