3.2 PATCH: Fully support parallel gnat1/gnatbind builds

[Richard Kenner]

    Which, I cannot resist pointing out, you refused to take a patch to
    eliminate that problem.

It eliminates *one particular* instance of the problem by disabling some
functionality (admittedly minor).  The point is that this is merely an
*example* of the sort of trouble you can get into by using different
compilers for each part of the build.