/usr/lib/x86_64-linux-gnu/libgnarl.so is in gnat-8 8-20180414-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgnarl-8.so.1
/usr/lib/x86_64-linux-gnu/libgnarl-8.so.1