reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/uml/linux.git/commit/?id=a7f7dbae94a5ae5cfbf2375e0d952c54b069fd7f
        git remote add uml https://git.kernel.org/pub/scm/linux/kernel/git/uml/linux
        git fetch --no-tags uml next
        git checkout a7f7dbae94a5ae5cfbf2375e0d952c54b069fd7f

        # 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 prepare