(toplevel) Fix dramatic breakage for ordinary crosses (related to program_transform_name)

[DJ Delorie]

> I dunno, sounds fine to me if it lets the subsequent real build
> go in parallel.

If you fill the job slots with busy-wait configures, there aren't any
slots left to put real builds in.

Of course, this is the point where we could conditionally take
advantage of gmake's "don't run these in parallel" syntax.