PATCH: Support x86 pseudo registers

[Eli Zaretskii]

> From: Pedro Alves <pedro@codesourcery.com>
> Date: Fri, 12 Mar 2010 18:20:10 +0000
> Cc: Daniel Jacobowitz <dan@codesourcery.com>,  hjl.tools@gmail.com,  msnyder@vmware.com
> 
> We could also stick to defaulting to the architecture meaning, and
> always provide $_pc, $_sp, $_fp, $_ps registers that always map to
> the generic versions.  That way, when there's a conflict,
> there's always an escape route.

I think it's a good idea.