/usr/lib/x86_64-linux-gnu/libgnatprj.so is in libgnatprj4.6-dev 4.6.4-0ubuntu5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgnatprj.so.4.6
/usr/lib/x86_64-linux-gnu/libgnatprj.so.4.6