DolphinWX: Add a progress dialog host command

Allows feedback from backends to be communicated to the user when
long-running operation are performed (e.g. shader compilation).

Source/Core/DolphinQt2/Host.cpp

@@ -84,6 +84,9 @@ void Host_YieldToUI()
 {
   qApp->processEvents(QEventLoop::ExcludeUserInputEvents);
 }
+void Host_UpdateProgressDialog(const char* caption, int position, int total)
+{
+}
 
 // We ignore these, and their purpose should be questioned individually.
 // In particular, RequestRenderWindowSize, RequestFullscreen, and