Define NvOptimusEnablement to tell the Nvidia driver we need high performance

Source/Core/DolphinWX/Src/Main.cpp

@@ -45,6 +45,15 @@
 
 #include <wx/intl.h>
 
+// Nvidia drivers >= v302 will check if the application exports a global
+// variable named NvOptimusEnablement to know if it should run the app in high
+// performance graphics mode or using the IGP.
+#ifdef WIN32
+extern "C" {
+	__declspec(dllexport) DWORD NvOptimusEnablement = 1;
+}
+#endif
+
 // ------------
 //  Main window