Make FrameBuffer::flush() a no-op when building outside of SDL.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/6cc8c3799ac

Widgets/FrameBuffer.cpp

@@ -90,9 +90,9 @@ RGBA32* FrameBuffer::scanline(int y)
 #endif
 }
 
+#ifdef USE_SDL
 void FrameBuffer::flush()
 {
-#ifdef USE_SDL
     SDL_UpdateWindowSurface(m_window);
-#endif
 }
+#endif

Widgets/FrameBuffer.h

@@ -25,7 +25,11 @@ public:
 
     RGBA32* scanline(int y);
 
+#ifdef USE_SDL
     void flush();
+#else
+    void flush() { }
+#endif
 
     static void initialize();