/usr/share/doc/ocaml-mingw-w64-x86-64/changelog.Debian.gz is in ocaml-mingw-w64-x86-64 4.00.1~20130426-3ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/ocaml-mingw-w64-x86-64/../flexdll/changelog.Debian.gz