Bump minimum Qt version (to build Qt Creator) to 5.11

Recent adaptations to Qt 5.13's API deprecations require using APIs
which were introduces in Qt 5.11.

Change-Id: I6c077d824c9ce716e019543b290c355a5d512fad
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/cpptools/cpptoolsreuse.cpp

@@ -323,18 +323,9 @@ bool fileSizeExceedsLimit(const QFileInfo &fileInfo, int sizeLimitInMb)
                     "C++ Indexer: Skipping file \"%1\" because it is too big.")
                         .arg(absoluteFilePath);
 
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 10, 0))
         QMetaObject::invokeMethod(Core::MessageManager::instance(), [msg]() {
             Core::MessageManager::write(msg, Core::MessageManager::Silent);
         });
-#else
-        QMetaObject::invokeMethod(Core::MessageManager::instance(),
-                                  "write",
-                                  Qt::QueuedConnection,
-                                  Q_ARG(QString, msg),
-                                  Q_ARG(Core::MessageManager::PrintToOutputPaneFlags,
-                                        Core::MessageManager::Silent));
-#endif
 
         qWarning().noquote() << msg;
         return true;