/usr/lib/x86_64-linux-gnu/libgnatcoll_gtk.so is in libgnatcoll-gtk1.6-dev 1.6gpl2014-9.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgnatcoll_gtk.so.1.6
/usr/lib/x86_64-linux-gnu/libgnatcoll_gtk.so.1.6