/usr/lib/ocaml/ld.conf is in ocaml-base-nox 4.05.0-10ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2
/usr/local/lib/ocaml/4.05.0/stublibs /usr/lib/ocaml/stublibs