reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://github.com/jimc/linux/commit/1f1e51f3a3c29c117e6a9f2f494018217d3b0cff
        git remote add jimc https://github.com/jimc/linux.git
        git fetch --no-tags jimc dd-classmap-fix-v4i
        git checkout 1f1e51f3a3c29c117e6a9f2f494018217d3b0cff
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash kernel/