qt: Add support for Haiku

* OpenAL backend is enabled by default on Haiku
* bswap include now makes use of builtins if they exist
* Use a local fgetws method for Haiku to avoid crashes
* OpenGL renderers are completely disabled on Haiku (they do not work)
* Software renderer is a widget, not a window on Haiku (fixes blank screen)
* Add option to disable System MIDI at compile time

src/qt/qt_main.cpp

@@ -162,6 +162,8 @@ int main(int argc, char* argv[]) {
     {
         return 0;
     }
+
+    fprintf(stderr, "Qt: version %s, platform \"%s\"\n", qVersion(), QApplication::platformName().toUtf8().data());
     ProgSettings::loadTranslators(&app);
 #ifdef Q_OS_WINDOWS
     auto font_name = QObject::tr("FONT_NAME");