[patch] for PRs 27639 and 26719

[Richard Kenner]

> My understanding is that this will prevent BIVs from being generated in 
> non-base types.

Well, that certainly seems right to me.  If a language wants to allow
arithmetic in non-base types, it's treading somewhat on thin ice in terms
of definitions of what it means and, at least until we get that better
defined, we shouldn't allow making IVs for them because that tends to
put pressure on precise definitions.

Do any languages actually generate such arithmetic?  I know that C and
Ada don't.