qt: Compatibility improvements

* Patch to build with Qt 5.11 and later by jriwanek
* Attempt to fix viewport on hardware renderers

src/qt/qt_main.cpp

@@ -134,7 +134,9 @@ int main(int argc, char* argv[]) {
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
     QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
 #endif
+#if QT_VERSION >= QT_VERSION_CHECK(5, 14, 0)
     QApplication::setHighDpiScaleFactorRoundingPolicy(Qt::HighDpiScaleFactorRoundingPolicy::PassThrough);
+#endif
     QApplication app(argc, argv);
     qt_set_sequence_auto_mnemonic(false);
     Q_INIT_RESOURCE(qt_resources);