device: fix warnings with Clang

src/device/display.h

@@ -25,6 +25,9 @@ struct DisplayMode
 /// @ingroup Device
 struct Display
 {
+	///
+	virtual ~Display() {};
+
 	/// Fills @a modes with all available display modes.
 	virtual void modes(Array<DisplayMode>& modes) = 0;
 

src/device/window.h

@@ -37,6 +37,9 @@ struct MouseCursor
 /// @ingroup Device
 struct Window
 {
+	///
+	virtual ~Window() {};
+
 	/// Opens the window.
 	virtual void open(u16 x, u16 y, u16 width, u16 height, u32 parent) = 0;