IA32: printing FP register variables

[Jim Blandy]

> I think you get more stable position designations by considering the
> position relative to the bottom of the stack.

True, but the whole problem is that we don't have any kind of frame
pointer for the FP stack, so we can't map from a bottom-relative
register number to a physical register number.  As Ben points out, you
can guess the bottom from the tags, but not reliably.