/usr/s390x-linux-gnu/lib/libgnatvsn.so is in libgnatvsn6-dev-s390x-cross 6.3.0-18cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/s390x-linux-gnu/lib/libgnatvsn.so.6
/usr/s390x-linux-gnu/lib/libgnatvsn.so.6