/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/ is in gcc-6-plugin-dev-arm-linux-gnueabi 6.4.0-17ubuntu1cross1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/aarch-common-protos.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/aout.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/arm-cores.def
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/arm-flags.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/arm-opts.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/arm-protos.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/arm.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/bpabi.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/elf.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/linux-eabi.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/linux-elf.h
/usr/lib/gcc-cross/arm-linux-gnueabi/6/plugin/include/config/arm/linux-gas.h