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
        # clang-21 might not be officially released. Try a lower version if installation fails.
        # https://github.com/morimoto/linux/commit/76ff9a5ac5f25b351b7ecc7743f4910aceb7bd1d
        git remote add morimoto https://github.com/morimoto/linux
        git fetch --no-tags morimoto string-helper-2025-07-18
        git checkout 76ff9a5ac5f25b351b7ecc7743f4910aceb7bd1d
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash drivers/md/dm-vdo/ drivers/media/cec/usb/pulse8/