reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git/commit/?id=cd29796e495160c05a672f3098dffe0fb6ae9daf
        git remote add driver-core https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
        git fetch --no-tags driver-core driver-core-testing
        git checkout cd29796e495160c05a672f3098dffe0fb6ae9daf
        # 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 kernel/time/