/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/ is in gcc-8-plugin-dev-powerpc64-linux-gnu 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/biarch64.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/default64.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/linux64.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/option-defaults.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/rs6000-builtin.def
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/rs6000-cpus.def
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/rs6000-opts.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/rs6000-protos.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/rs6000.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/secureplt.h
/usr/lib/gcc-cross/powerpc64-linux-gnu/8/plugin/include/config/rs6000/sysv4.h