reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/commit/?id=aa31e8a044a62529f5afa3275d63b5019142c901
        git remote add ast-bpf https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git
        git fetch --no-tags ast-bpf arena
        git checkout aa31e8a044a62529f5afa3275d63b5019142c901
        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