[PATCH] [CodeGen] Don't cast and use SizeTy instead of Int32Ty when constructing {extract, insert} vector element instructions.

[Chandler Carruth]

This seems like a strict improvement. Is there ever a case where the incoming index size would not be SizeTy? I wonder if we should use its type directly, even if just for clarity, to indicate that the goal is to use whatever integer size we already have.

http://reviews.llvm.org/D3974