When creating libraries using ocamlopt -a, it seems that it is
necessary to give the modules on the command line in such an order
that all inter-module references are to modules which precede on the
command line.  Otherwise, I get link-time errors when using the
library.

In my case, there are no cyclic module references, and there is no
requirement that the modules are initialized in a particular order
(beyond that what is implied by explicit references), so a simple
topological sort could come up with a proper ordering.  Is there some
way to have ocamlopt do this for me?