[PATCH] [mips] Promote all integral/enumeration types to the GPR width

[Daniel Sanders]

>>! In D5961#4, @atanasyan wrote:
> Just curious, does it have a sense to zero- or sign- extend 32-bit types in case of O32 ABI? For example, PowerPC does the similar things in case of 64-bit ABI only `PPC64_SVR4_ABIInfo::isPromotableTypeForABI`.

I couldn't find a functional difference between 'i32' and 'i32 signext' on O32 (and similarly between 'i32' and 'i32 zeroext'). This makes sense because sign-extending i32 to i32 is a noop. I couldn't think of any benefits to using 'i32' for O32 and 'i32 signext' for N32/N64 so I decided to simplify the code.

http://reviews.llvm.org/D5961