reproduce (this is a W=1 build):
        git remote add willy-pagecache git://git.infradead.org/users/willy/pagecache
        git fetch --no-tags willy-pagecache headers
        git checkout ad78a547dcd8964e9c6ec0e89183d6cd228d2ad6

        # install um cross compiling tool for clang build
        # apt-get install binutils-um-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=$HOME/0day COMPILER=clang-24 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang-24 ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=um SHELL=/bin/bash fs/