build fixes for most WinRT-related files

Still TODO: getting the D3D11 renderer back up and running in VC 2012.

src/filesystem/winrt/SDL_sysfilesystem.cpp

@@ -2,7 +2,7 @@
    TODO, WinRT: remove the need to compile this with C++/CX (/ZW) extensions, and if possible, without C++ at all
 */
 
-#include "SDL_config.h"
+#include "../../SDL_internal.h"
 
 #ifdef __WINRT__