InputConfigDiag: Update for the new expression language

Modify the buttons and editor interface for the new expression
language, like the new op name for add, the new device name syntax,
and add new editing features, like simple selection behavior on
unary ops.

Source/Core/DolphinWX/Src/InputConfigDiag.h

@@ -113,6 +113,7 @@ private:
 	GamepadPage* const		m_parent;
 	wxStaticText*		m_bound_label;
 	DeviceQualifier	m_devq;
+	bool GetExpressionForSelectedControl(wxString &expr);
 };
 
 class ExtensionButton : public wxButton