ACATS c460008 and VRP (was: Bootstrap failure on trunk: x86_64-linux-gnu)

[Richard Kenner]

> Richard, Arnaud, could you check amongst GNAT experts if for such types
> (non power of two modulus), it's not worth enabling overflow checks by
> default now that we have VRP doing non trivial optimisations? People
> using non power of two modulus are not caring for performance anyway, so
> having a compliant implementation by default won't harm.

I don't think that either of us are the best people to ask, but my sense
is that it's not a great idea to have the default overflow handling differ
between types.  For one thing, what option would then disable overflow
checking for those types?

-gnato is required for ACATS tests because you need -gnato for RM compliance.