/usr/lib/gcc-cross/mips64-linux-gnuabi64/8/libobjc.so is in libobjc-8-dev-mips64-cross 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/mips64-linux-gnuabi64/8/../../../../mips64-linux-gnuabi64/lib/libobjc.so.4