/usr/lib/x86_64-linux-gnu/libmirclient-debug-extension.so is in libmirclient-debug-extension-dev 0.26.3+16.04.20170605-0ubuntu1.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmirclient-debug-extension.so.1