/usr/lib/gcc-cross/mips64-linux-gnuabi64/5/n32/libobjc.so is in libn32objc-5-dev-mips64-cross 5.5.0-12ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/mips64-linux-gnuabi64/5/n32/../../../../../mips64-linux-gnuabi64/lib32/libobjc.so.4