reproduce:
        # https://github.com/jcmvbkbc/linux-xtensa/commit/af2c0b346e49361fee95cbd8a73eb6430b4c5f80
        git remote add jcmvbkbc-xtensa https://github.com/jcmvbkbc/linux-xtensa
        git fetch --no-tags jcmvbkbc-xtensa xtensa-6.8-rc2-esp32
        git checkout af2c0b346e49361fee95cbd8a73eb6430b4c5f80
        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