/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/ is in gcc-7-plugin-dev-aarch64-linux-gnu 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-arches.def
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-cores.def
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-elf.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-fusion-pairs.def
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-linux.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-opts.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-protos.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64-tuning-flags.def
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/aarch64.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/biarchlp64.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/arm/
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/arm/aarch-common-protos.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/dbxelf.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/elfos.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/glibc-stdint.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/gnu-user.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/initfini-array.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/linux-protos.h
/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/linux.h