Code style: add missed explicit 'this->'

CMake uses explicit 'this->' style. Using custom clang-tidy check we can
detect and fix places where 'this->' was missed.

Source/cmLinkedTree.h

@@ -133,9 +133,9 @@ public:
     return iterator(const_cast<cmLinkedTree*>(this), 0);
   }
 
-  iterator Push(iterator it) { return Push_impl(it, T()); }
+  iterator Push(iterator it) { return this->Push_impl(it, T()); }
 
-  iterator Push(iterator it, T t) { return Push_impl(it, std::move(t)); }
+  iterator Push(iterator it, T t) { return this->Push_impl(it, std::move(t)); }
 
   bool IsLast(iterator it) { return it.Position == this->Data.size(); }