reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git/commit/?id=9b1e70e8f9ec4b5c6ce7fa774a0023bb6894c686
        git remote add cxl https://git.kernel.org/pub/scm/linux/kernel/git/cxl/cxl.git
        git fetch --no-tags cxl for-7.3/cxl-type2-enabling
        git checkout 9b1e70e8f9ec4b5c6ce7fa774a0023bb6894c686

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash