AM33: Use macros instead of register number constants

[Alexandre Oliva]

On Apr 27, 2000, Jeffrey A Law <law@cygnus.com> wrote:

> You should probably move the definitions of those macros before their
> first uses.

Ok.  Is this necessary from a point-of-view of portability, or is it
just a matter of making the code clearer?

I've realized that I had missed the _REGNUM macros, so I've addressed
this issue, renamed the new (FIRST|LAST)_*_REG macros to *_REGNUM and
I'm now checking in the following patch.