For areVectorOperandsLaxBitCastable(), only return false if both opearands are vector types
and add a diagnostic when the operand is a vector and non-scalar value.

rdar://15722301

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198680 91177308-0d34-0410-b5e6-96231b3b80d8