reproduce:
        # https://github.com/sean-jc/linux/commit/cc63298ca9d5d24b37a730484b8a71b359652f46
        git remote add sean-jc https://github.com/sean-jc/linux
        git fetch --no-tags sean-jc x86/gnu_source
        git checkout cc63298ca9d5d24b37a730484b8a71b359652f46
        make W=1 O=/tmp/kselftest headers
        make W=1 O=/tmp/kselftest -C tools/testing/selftests
        make W=1 O=/tmp/kselftest -C tools/testing/selftests/bpf