reproduce:
        # https://github.com/jimc/linux/commit/33f283020361f21a73ef51dfa75a81b57a217177
        git remote add jimc https://github.com/jimc/linux.git
        git fetch --no-tags jimc lukas-v3.2
        git checkout 33f283020361f21a73ef51dfa75a81b57a217177
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs