/usr/lib/gcc-cross/mipsel-linux-gnu/7/n32/libobjc.so is in libn32objc-7-dev-mipsel-cross 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/mipsel-linux-gnu/7/n32/../../../../../mipsel-linux-gnu/lib32/libobjc.so.4