Patch for faster memcpy on MIPS

[Ellcey, Steve]

> I think I will add Richard Sandiford too.  I don't know why regdef.h in newlib would use the same 
> register names for the EABI as for the N32 and 64 bit ABIs but there may be reasons I am not
> aware of.
> 
> I have reproduced the problem, I am going to try and rebuild after removing
> '|| _MIPS_SIM==_ABIEABI' from regdef.h and see if things build once I have done that.

> Steve Ellcey
> sellcey@mips.com

Well, that didn't work.  I will have to spend some more time on figuring out exactly what is going
on.

Steve Ellcey
sellcey@mips.com