reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?id=d7aa9525f39c3c2f5520db30b40edb9c8f13774e
        git remote add rafael-pm https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git
        git fetch --no-tags rafael-pm pm-sleep-testing
        git checkout d7aa9525f39c3c2f5520db30b40edb9c8f13774e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 prepare