/usr/lib/gcc-cross/mips-linux-gnu/6/n32/libatomic.so is in libn32gcc-6-dev-mips-cross 6.3.0-18cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/mips-linux-gnu/6/n32/../../../../../mips-linux-gnu/lib32/libatomic.so.1