reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git/commit/?id=a0384236cb3e082d9b29da494e71db6275aef526
        git remote add ast-bpf https://git.kernel.org/pub/scm/linux/kernel/git/ast/bpf.git
        git fetch --no-tags ast-bpf rust-bpf
        git checkout a0384236cb3e082d9b29da494e71db6275aef526

        # install um cross compiling tool for clang build
        # apt-get install binutils-um-linux-gnu
        # clang-23 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=$HOME/0day COMPILER=clang-23 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-23 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um SHELL=/bin/bash kernel/bpf/