reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git/commit/?id=843542230b45c042286f208e66c0c473f03abd99
        git remote add thomas-weissschuh https://git.kernel.org/pub/scm/linux/kernel/git/thomas.weissschuh/linux.git
        git fetch --no-tags thomas-weissschuh b4/kunit-kselftests
        git checkout 843542230b45c042286f208e66c0c473f03abd99
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash lib/