Long multiplication and BigInteger.mulAdd on x86_32

[Hiroshi Yamauchi]

Hi Christian,

> I think that's a good change.  I have two comments: personally I prefer to
> use assembler instructions directly in the ins_encode than writing
> very-hard-to-read enc_class methods and the predicates are kind of ugly, but
> I don't know if that could be done any better.

I'll see if I can do it better that way.

> Maybe, given that we probably support more 32-bit architectures in the
> future, we could model such instructions in ideal (e.g. in a pass that's
> only used on 32-bit).

I agree that it'd be easier and probably more effective to apply the
same optimization at the ideal graph level.

Thanks,
Hiroshi