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/libs/utils/algorithm.h

@@ -1262,6 +1262,7 @@ OutputIterator set_union(InputIterator1 first1,
 
 // Replacement for deprecated Qt functionality
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 template <class T>
 QSet<T> toSet(const QList<T> &list)
 {
@@ -1271,6 +1272,7 @@ QSet<T> toSet(const QList<T> &list)
     return QSet<T>(list.begin(), list.end());
 #endif
 }
+#endif
 
 template<class T>
 QSet<T> toSet(const QVector<T> &vec)