reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git/commit/?id=a5c846605296d2d543e83e87dd01e3ab12dcd567
        git remote add jlayton https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git
        git fetch --no-tags jlayton kdevops
        git checkout a5c846605296d2d543e83e87dd01e3ab12dcd567
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um SUBARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=um SUBARCH=i386 SHELL=/bin/bash fs/