reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/broonie/ci.git/commit/?id=b2c35cdee47a019777aa9f9216b49a6392cc79e3
        git remote add broonie-ci https://git.kernel.org/pub/scm/linux/kernel/git/broonie/ci.git
        git fetch --no-tags broonie-ci arm64-gcs
        git checkout b2c35cdee47a019777aa9f9216b49a6392cc79e3

        # install arm64 cross compiling tool for clang build
        # apt-get install binutils-aarch64-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=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-21 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash arch/arm64/kernel/