[PATCH 21.5] Ensure correct finder* is used during build

[Stephen J. Turnbull]

Ville Skyttä writes:

 > Makes sense to me, but I've never tried that - hence narrowed the
 > patch to what I've tested.  finder-inf.el is the only case where
 > I've seen this kind of a problem but it could very well cause
 > unwanted things elsewhere too.

OK.  I'll try it locally, but that's not much of a test.  Before
committing, please give Mike a few days to respond.