Change `MDNode::isDistinct()` to only apply to 'distinct' nodes (not
temporaries), and introduce `MDNode::isUniqued()` and
`MDNode::isTemporary()` for the other two possibilities.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226482 91177308-0d34-0410-b5e6-96231b3b80d8