reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        git remote add klassert-ipsec-next https://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next.git
        git fetch klassert-ipsec-next master
        git checkout klassert-ipsec-next/master
        b4 shazam https://lore.kernel.org/r/ZmlmTTYL6AkBel4P@gauss3.secunet.de
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-19 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-19 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash net/xfrm/