[Coco] gcc m6809 update

[James Dessart]

I will soon be undertaking the project of updating gcc for the m6809 to be
based on the m68hc11 code, since the processors are very similar.  This
will be in an effort to increase the number of "registers" available, by
using a set of locations on a page boundary, and the direct addressing
mode.

Why?  Well, then it'll be easier to use floating point math.  gcc includes
some support for soft floting point, and the code looks complete for basic
operations.

Also, I'll be updating the machine description in CVS as soon as possible.
The old one is buggy, and contains invalid code for generating subtraction
assembly.  I received a fix from Eric Botcazou, the guy who I got the
files from originally.

James