IA32: printing FP register variables

[Jim Blandy]

Hmm.  What other IA32 compilers produce STABS?  How do they number FP
registers?

If GDB can find the base of the FP stack reliably, using the method
that Ben Combee suggests, then we don't need LRS at all to describe
variables' homes.  If we simply number the FP registers relative to
the base of the FP stack, their names won't change as insns push and
pop FP values.

So the only work to be done is:
- GCC needs to propage the register/variable association through the
  stackifier, so it can produce coherent debug output.
- GDB needs to use Ben Combee's tactic for finding the base of the
  stack.