/usr/s390x-linux-gnu/lib/libgnat.so is in gnat-6-s390x-linux-gnu 6.4.0-17ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/s390x-linux-gnu/lib/libgnat-6.so.1
/usr/s390x-linux-gnu/lib/libgnat-6.so.1