reproduce:
        # https://github.com/intel/linux-intel-lts/commit/b2eccf8f49c2ecfbd40001948e14ebb824a1ac60
        git remote add intel-lts https://github.com/intel/linux-intel-lts.git
        git fetch --no-tags intel-lts pr/56
        git checkout b2eccf8f49c2ecfbd40001948e14ebb824a1ac60
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs