Altivec + 16 byte alignment

[Robert Dewar]

> I think that's a *very* bad idea: as you say, what stor-layout.c does is
> very complex.  There will be a significant amount of work to keep some other
> code in sync with it.

I must say I agree with Richard here (I have often wanted to move layout into
the front end of Ada, but Richard has always managed to convince me this is
a bad idea). Can you say *why* you are making this decision:

    The C parser I'm working on won't use it to lay out types, since I don't
    use trees.  I'll have to ensure that what stor-layout.c does (during
    lowering) is the same as what I've done.  At least in an initial
    implementation.