ARCH_NUM_REGS

[David Taylor]

In addition to NUM_REGS and NUM_PSEUDO_REGS, there's the define
ARCH_NUM_REGS -- which by default is the same as NUM_REGS.

One presumes that ARCH_NUM_REGS is meant to have slightly different
semantics than NUM_REGS, but it isn't documented and it doesn't seem
to be used in any consistent fashion that I've discerned.

So, what are the intended semantics of ARCH_NUM_REGS?

According to the ChangeLog's ARCH_NUM_REGS was created in 1994 by Stan
Shebs.