[PATCH] m32c-tdep.c: Add virtual_frame_pointer function

[DJ Delorie]

> You probably should change legacy_virtual_frame_pointer to check for
> SP_REGNUM < NUM_REGS + NUM_PSEUDO_REGS instead.

Note that m32c has two stack pointers, and the one that's used depends
on the CPU flags.  This is separate from the flag that determines
which register bank is in use.