Use an older compiler for a port

Hello.

We've got an internal-use port which compiles on 14.0 and 13.2, but not 
on 13.3. I suspect the culprit to be LLVM 17.

Is there I way I can force the port to use LLVM 16 (or earlier)?
I tried "USES= llvm:16", but that didn't do the trick.

Thanks is advance.

  bye
	av.

P.S.
Of course fixing the port would be the best thing, but it's not going to 
be easy and in any case it's going away in some month, so it's not worth it.