/usr/lib/gcc-cross/sh4-linux-gnu/7/libatomic.so is in libgcc-7-dev-sh4-cross 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/sh4-linux-gnu/7/../../../../sh4-linux-gnu/lib/libatomic.so.1