[Ada] Bootstrapping mainline GNAT fails

[Richard Kenner]

    Since the problem didn't manifest with Richard's test program, I
    imagine it's an extreme corner case, 

Yes, that is peculiar, because in the ia64 case, that test program didn't
work either.

    possibly with bad interactions with the C library as well (there is
    some concern over whether glibc 2.2 works properly with 2.8.1-era
    GCC).

Seems unlikely, since I don't see why glibc should get involved.

    If exceptions are used only to signal fatal errors, 

They aren't.  That's the point.