SCO OpenServer / UnixWare port update

[Kean Johnston]

> Because in some cases sizeof(_Unwind_Ptr) != sizeof(_Unwind_Word).
> You should remember that this is, in effect,
> 
>   return (_Unwind_Word)(_Unwind_Ptr) context->cfa;
> 
> which is in fact exactly what I wanted.  This is important for
> systems like MIPS n32, and some SH5 variants.
Aha. Ok then, can I make it explicitly do that? I had a
bootstrap error using the native cc becuase it didn't like
the implied conversion.

> We're trying to get rid of these little files, not create more.
Ok. I will adjust the SCO targets to use tm_defines instead.
The only other target that is using usegas.h is sequent-ptx
and I can make a similar adjustment there and then remove
usegas.h as well.

Kean