reproduce (this is a W=1 build):
        # https://github.com/sean-jc/linux/commit/d2dd49c5f92f1ccb2f22e281942dfb7771e27bc2
        git remote add sean-jc https://github.com/sean-jc/linux
        git fetch --no-tags sean-jc x86/gmem_inplace
        git checkout d2dd49c5f92f1ccb2f22e281942dfb7771e27bc2

        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=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-8.5.0 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash