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/stringtable.cpp

@@ -92,8 +92,10 @@ QString StringTablePrivate::insert(const QString &string)
     if (string.isEmpty())
         return string;
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 #ifndef QT_NO_UNSHARABLE_CONTAINERS
     QTC_ASSERT(const_cast<QString&>(string).data_ptr()->ref.isSharable(), return string);
+#endif
 #endif
 
     m_stopGCRequested.fetchAndStoreAcquire(true);