reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?id=b556b4a52f0a9b57d906dbb3bd63cebe6159e3e7
        git remote add ardb https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git
        git fetch --no-tags ardb efi-libstub-native-utf16
        git checkout b556b4a52f0a9b57d906dbb3bd63cebe6159e3e7

        # install riscv cross compiling tool for clang build
        # apt-get install binutils-riscv64-linux-gnu
        # clang-24 might not be officially released. Try a lower version if installation fails.
        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=$HOME/0day COMPILER=clang-24 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-24 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash drivers/firmware/efi/libstub/