reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # install um cross compiling tool for clang build
        # apt-get install binutils-um-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git/commit/?id=5214acb8d02febb2238f4f74dc27cf5bc460c206
        git remote add melver https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git
        git fetch --no-tags melver misc
        git checkout 5214acb8d02febb2238f4f74dc27cf5bc460c206
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-18 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-18 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um SHELL=/bin/bash