/usr/lib/gcc-cross/aarch64-linux-gnu/7/plugin/include/config/aarch64/ 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/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