/usr/lib/gcc/x86_64-linux-gnu/ is in libobjc-6-dev 6.4.0-17ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc/x86_64-linux-gnu/6/
/usr/lib/gcc/x86_64-linux-gnu/6/include/
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/NXConstStr.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/Object.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/Protocol.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/message.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/objc-decls.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/objc-exception.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/objc-sync.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/objc.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/runtime.h
/usr/lib/gcc/x86_64-linux-gnu/6/include/objc/thr.h
/usr/lib/gcc/x86_64-linux-gnu/6/libobjc.a
/usr/lib/gcc/x86_64-linux-gnu/6/libobjc.so
/usr/lib/gcc/x86_64-linux-gnu/6/libobjc_gc.a
/usr/lib/gcc/x86_64-linux-gnu/6/libobjc_gc.so