reproduce (this is a W=1 build):
        git remote add stefandoesinger-zx297520 https://gitlab.com/stefandoesinger/zx297520-kernel
        git fetch --no-tags stefandoesinger-zx297520 mfd
        git checkout 7b95ce97d9a13b0d3b2ca1c45b6bacc090309344

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash