reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git/commit/?id=d766ca01c208bdf0f36098607efe1e250ccf41c5
        git remote add lee-mfd https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git
        git fetch --no-tags lee-mfd ib-mfd-input-6.18
        git checkout d766ca01c208bdf0f36098607efe1e250ccf41c5
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arc SHELL=/bin/bash drivers/mfd/