Darwin as primary platform

[Andrew Pinski]

> FWIW I think a 64-bit native version might be nice as a separate  
> target, but I've been told there's no real advantage there either on  
> ppc.

For PPC64-Darwin, there might be an advantage having a better ABI passing around
structs but other than that I don't think there is one unless GCC is running
out of memory which IIRC happens on Bradley's code a lot.

-- Pinski