SDL_SYS_IsXInputGamepad_DeviceIndex() is only available if SDL_JOYSTICK_XINPUT is true.

src/joystick/SDL_sysjoystick.h

@@ -108,8 +108,10 @@ extern SDL_JoystickGUID SDL_SYS_JoystickGetDeviceGUID(int device_index);
 /* Function to return the stable GUID for a opened joystick */
 extern SDL_JoystickGUID SDL_SYS_JoystickGetGUID(SDL_Joystick * joystick);
 
+#if SDL_JOYSTICK_XINPUT
 /* Function returns SDL_TRUE if this device is an XInput gamepad */
 extern SDL_bool SDL_SYS_IsXInputGamepad_DeviceIndex(int device_index);
+#endif
 
 #endif /* _SDL_sysjoystick_h */