/usr/share/doc/libmysqlclient-dev/changelog.Debian.gz is in libmysqlclient-dev 5.5.54-0ubuntu0.12.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmysqlclient-dev/../libmysqlclient18/changelog.Debian.gz