reproduce:
        git remote add android-common https://android.googlesource.com/kernel/common
        git fetch --no-tags android-common android12-trusty-5.10
        git checkout 45506ac6c1c6ad0246636b623288e414c9dbefff
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs