reproduce (this is a W=1 build):
        git remote add netfilter-nf https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git
        git fetch netfilter-nf main
        git checkout netfilter-nf/main
        b4 shazam https://lore.kernel.org/r/20260403193929.89449-1-marino.dzalto@gmail.com

        # 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 net/netfilter/