IA32: printing FP register variables

[Jim Blandy]

The disadvantages of base-relative numbering are:
- It's unexpected.  Every existing system saves registers in
  top-relative order.  The IA32's FSAVE instruction saves them
  top-relative.  Assembly code refers to them top-relative.
- I'm not sure how to implement something like "print $st0".
- It requires straightforward but non-trivial support in GDB's
  target-specific code to find the FP stack base and load the register
  array properly.

In that light, it had better save us a significant amount of space
over top-relative numbering if we're going to go to the trouble.  But
we have no idea how much space it will save.

Once the other internal work is done, would the EGCS folks be willing
to experiment with both, and give us some sense of how much difference
it makes?

If the savings are negligible, I'm not sure it's worth the hair.