reproduce (this is a W=1 build):
        # https://github.com/ClangBuiltLinux/linux/commit/b073116da78daa4548a491eba6508141a9b350dc
        git remote add clangbuiltlinux https://github.com/ClangBuiltLinux/linux
        git fetch --no-tags clangbuiltlinux question_mark_operator
        git checkout b073116da78daa4548a491eba6508141a9b350dc

        # install s390 cross compiling tool for clang build
        # apt-get install binutils-s390x-linux-gnu
        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=$HOME/0day COMPILER=clang-18 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-18 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash