C. Compare vector sizes using their raw element size instead of

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