Update SDL2 to latest hg (fbfacc66c65c)

libs/SDL2/include/SDL_gamecontroller.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2017 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2018 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -175,6 +175,14 @@ extern DECLSPEC SDL_bool SDLCALL SDL_IsGameController(int joystick_index);
  */
 extern DECLSPEC const char *SDLCALL SDL_GameControllerNameForIndex(int joystick_index);
 
+/**
+ *  Get the mapping of a game controller.
+ *  This can be called before any controllers are opened.
+ *
+ *  \return the mapping string.  Must be freed with SDL_free().  Returns NULL if no mapping is available
+ */
+extern DECLSPEC char *SDLCALL SDL_GameControllerMappingForDeviceIndex(int joystick_index);
+
 /**
  *  Open a game controller for use.
  *  The index passed as an argument refers to the N'th game controller on the system.