IR: Make temporary nodes distinct

Change the return of `MDNode::isDistinct()` for `MDNode::getTemporary()`
to `true`.  They aren't uniqued.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225646 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Metadata.h

@@ -651,7 +651,9 @@ public:
   ///
   /// Distinct nodes are not uniqued, and will not be returned by \a
   /// MDNode::get().
-  bool isDistinct() const { return IsDistinctInContext; }
+  bool isDistinct() const {
+    return isStoredDistinctInContext() || isa<MDNodeFwdDecl>(this);
+  }
 
 protected:
   /// \brief Set an operand.