/usr/lib/gcc-cross/powerpc-linux-gnu/5/libatomic.so is in libgcc-5-dev-powerpc-cross 5.4.0-6ubuntu1~16.04.9cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/powerpc-linux-gnu/5/../../../../powerpc-linux-gnu/lib/libatomic.so.1