Gather file infos synchronously on no-thread builds

QFileInfoGatherer is implicitly dependent on threads - there are
no compile guards but the file scan loop runs on a thread.
Make it gather file infos sync if threads are not enabled so that
signals are properly fired from it on filesystem scans.

Fixes: QTBUG-85445
Backport-to: 6.4 5.15
Change-Id: I55f37497aa97bde2fc0fa2dece33c95acc870e99
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/gui/itemmodels/qfileinfogatherer.cpp

@@ -121,9 +121,13 @@ void QFileInfoGatherer::fetchExtendedInformation(const QString &path, const QStr
         }
         loc = this->path.lastIndexOf(path, loc - 1);
     }
+#if QT_CONFIG(thread)
     this->path.push(path);
     this->files.push(files);
     condition.wakeAll();
+#else // !QT_CONFIG(thread)
+    getFileInfos(path, files);
+#endif // QT_CONFIG(thread)
 
 #if QT_CONFIG(filesystemwatcher)
     if (files.isEmpty()