qt: Compatibility improvements

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

src/qt/qt_softwarerenderer.cpp

@@ -76,7 +76,11 @@ void SoftwareRenderer::onPaint(QPaintDevice* device) {
 
     QPainter painter(device);
     painter.setRenderHint(QPainter::SmoothPixmapTransform, video_filter_method > 0 ? true : false);
+#if QT_VERSION >= QT_VERSION_CHECK(5, 14, 0)
     painter.fillRect(0, 0, device->width(), device->height(), QColorConstants::Black);
+#else
+    painter.fillRect(0,0, device->width(), device->height(), Qt::black);
+#endif
     painter.setCompositionMode(QPainter::CompositionMode_Plus);
     painter.drawImage(destination, *images[cur_image], source);
 }