direct3d11: fix video position on Windows Phone and WinRT

the SwapChain dimensions are read from shared private data in the DXGI swap chain
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/video_output/msw/common.h

@@ -69,6 +69,11 @@ typedef struct
 } d3d_quad_t;
 #endif
 
+#if VLC_WINSTORE_APP
+extern const GUID GUID_SWAPCHAIN_WIDTH;
+extern const GUID GUID_SWAPCHAIN_HEIGHT;
+#endif
+
 /*****************************************************************************
  * vout_sys_t: video output method descriptor
  *****************************************************************************