reproduce:
        # https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?id=09459967e775f758f42e09b2540c993061089327
        git remote add jic23-iio https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git
        git fetch --no-tags jic23-iio testing
        git checkout 09459967e775f758f42e09b2540c993061089327
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        # install Sphinx 2.4.4
        make htmldocs