Fixed bug 3517 - Compiler warnings with gcc -Wstrict-prototypes

felix

Compiling even a simple SDL2 'hello world' program with gcc -Wstrict-prototypes (GCC 6.2.1) results in warnings like:

/usr/include/SDL2/SDL_gamecontroller.h:143:1: attention : function declaration isn't a prototype [-Wstrict-prototypes]
 extern DECLSPEC int SDLCALL SDL_GameControllerNumMappings();
 ^~~~~~

It seems there is a missing 'void' between the parentheses.

src/joystick/SDL_gamecontroller.c

@@ -891,7 +891,7 @@ SDL_GameControllerAddMapping(const char *mappingString)
  *  Get the number of mappings installed
  */
 int
-SDL_GameControllerNumMappings()
+SDL_GameControllerNumMappings(void)
 {
     int num_mappings = 0;
     ControllerMapping_t *mapping;