C. Compare vector sizes using their raw element size instead of
getTypeSize (which rounds up sizes) in order to issue diagnostics 
when casting to mismatched vector sizes; instead of crashing in IRGen.
// rdar:// 16196902. Reviewed offline by John McCall.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203175 91177308-0d34-0410-b5e6-96231b3b80d8