Alan Schmitt <alan.schmitt@polytechnique.org> writes:

[...]

> My goal is to be able to compile the OS GUI version of Unison on a
> single machine. Right now, using my intel-based notebook, I'm able to
> compile a version that runs both on 10.4 and 10.5, but only on intel.

[...]

> I think I remember an old message addressing this, but I have not been
> able to find it.

You might be referring to this message:

http://thread.gmane.org/gmane.comp.lang.caml.general/38930

The cute trick consists in building a PPC version of OCaml on a PPC
machine, and then copying it over to your Intel machine. It will run
fine (albeit slowly) under Rosetta, and generate PPC executables.

Michel.