[MS ABI] Be a little more defensive wrt vector types

[MS ABI] Be a little more defensive wrt vector types

We probably shouldn't say that all appropriately sized vector types are
intel vector types (i.e. __m128, etc.) as they don't exist for all
architectures.  While this is largely academic, it'd save some debugging
if we supported such a platform.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@238731 91177308-0d34-0410-b5e6-96231b3b80d8