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://github.com/zen-kernel/zen-kernel/commit/a1f04ded36fb527bc23efdb969b1893c82e61a6e
        git remote add zen https://github.com/zen-kernel/zen-kernel
        git fetch --no-tags zen 6.12/bbr3
        git checkout a1f04ded36fb527bc23efdb969b1893c82e61a6e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-20 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash net/ipv4/