/usr/lib/gcc-cross/arm-linux-gnueabihf/4.8/libatomic.so is in libgcc-4.8-dev-armhf-cross 4.8.5-4ubuntu1cross2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/arm-linux-gnueabihf/4.8/../../../../arm-linux-gnueabihf/lib/libatomic.so.1