reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu.git/commit/?id=f39ca69b9539fbc15fc68adf47ba721cb9c6a6e1
        git remote add gerg-m68knommu https://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu.git
        git fetch --no-tags gerg-m68knommu dt
        git checkout f39ca69b9539fbc15fc68adf47ba721cb9c6a6e1

        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=m68k olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash arch/m68k/kernel/ drivers/tty/serial/