/usr/lib/x86_64-linux-gnu/libgnatcoll_readline.so is in libgnatcoll-readline16.1.0-dev 17.0.2017-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgnatcoll_readline.so.17.0.2017