Add some uses of std::move in constructors and simple functions for pass-by-value arguments

src/Val.h

@@ -1563,7 +1563,7 @@ public:
      * @return  True if the element was inserted or false if the element was
      * the wrong type.
      */
-    bool Append(ValPtr element) { return Insert(Size(), element); }
+    bool Append(ValPtr element) { return Insert(Size(), std::move(element)); }
 
     // Removes an element at a specific position.
     bool Remove(unsigned int index);