core changes for mep port

[NickK]

In addition, my current email conversation with Dorit about GPU 
integration would be better suited to high level optimisation and code 
separation with multiple backends.

Eric Christopher wrote:
>>
>> This and the register changes come close to multi-arch gcc. Is that a
>> direction we want to go? Historically we have not tried to support
>
> Personally I'd love to see us go this way if it doesn't inconvenience 
> us too much.
> From what I remember of the MeP port it was pretty clean and wouldn't
> be an inconvenience.
>
> -eric
>
>