Minor dubious fix for am33 gas

[Alexandre Oliva]

On Apr  1, 2000, Jeffrey A Law <law@cygnus.com> wrote:

> Though as you note, recognizing them may cause problems with older
> am30/mn10300 code if they used those names for in assembly code.

In fact, we'd already cause trouble compiling mn10300 code containing
symbols such as `r0'.  This patch fixes this bug.  While I was at it,
I cleaned up some constants so as to use #defines instead of
literals.  Ok to install?  Head and branch?

BTW, the extra register names need not be defined at all.  The code to
handle them is all already in place.  Adding them to the array was not
needed.