/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/ is in gcc-5-plugin-dev 5.5.0-12ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/dbxelf.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/elfos.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/glibc-stdint.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/gnu-user.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/att.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/biarch64.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/gnu-user-common.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/gnu-user64.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/i386-opts.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/i386-protos.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/i386.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/linux-common.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/linux64.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/stringop.def
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/unix.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/x86-64.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/i386/x86-tune.def
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/initfini-array.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/linux-android.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/linux-protos.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/linux.h
/usr/lib/gcc/x86_64-linux-gnu/5/plugin/include/config/vxworks-dummy.h