reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # install s390 cross compiling tool for clang build
        # apt-get install binutils-s390x-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/commit/?id=8708f0a685326c02e1927a7a18aa78bd58bef8b1
        git remote add rppt https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git
        git fetch --no-tags rppt mm_init/mem_init/v0.1
        git checkout 8708f0a685326c02e1927a7a18aa78bd58bef8b1
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-15 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-15 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash arch/s390/mm/