/usr/share/doc/libgmp-dev/changelog.Debian.gz is in libgmp-dev 2:5.0.2+dfsg-2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgmp-dev/../libgmp10/changelog.Debian.gz
/usr/share/doc/libgmp-dev/../libgmp10/changelog.Debian.gz