reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/commit/?id=e56e2af8867c3690298e889b9febb1cb4d712341
        git remote add ebiggers https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git
        git fetch --no-tags ebiggers wip-crc
        git checkout e56e2af8867c3690298e889b9febb1cb4d712341
        # 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 lib/