/usr/lib/gcc-cross/aarch64-linux-gnu/4.9/libobjc.so is in libobjc-4.9-dev-arm64-cross 4.9.3-13ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/aarch64-linux-gnu/4.9/../../../../aarch64-linux-gnu/lib/libobjc.so.4