Partial compile fix for current Qt dev and/or Qt 6

This does not cover Utils::MapReduceOption with QVector, and code
that's not compiled on my machine.

Change-Id: Ib63923985c52b1bb74e5ec2068a2bb37469ac618
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cpptools/functionutils.h

@@ -27,9 +27,7 @@
 
 #include "cpptools_global.h"
 
-QT_BEGIN_NAMESPACE
-template <class> class QList;
-QT_END_NAMESPACE
+#include <QList>
 
 namespace CPlusPlus {
 class Class;