CodeGen: Stop treating vectors as aggregates

Fix a crash in SjLjEHPrepare::lowerIncomingArguments caused by treating
VectorType like an aggregate.  It's first-class!

<rdar://problem/15854596>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199768 91177308-0d34-0410-b5e6-96231b3b80d8