Fixed the header guard in the darwin SDL_sysjoystick_c.h file.
diff --git a/src/joystick/darwin/SDL_sysjoystick_c.h b/src/joystick/darwin/SDL_sysjoystick_c.h
index 7bc20d0..0fefa26 100644
--- a/src/joystick/darwin/SDL_sysjoystick_c.h
+++ b/src/joystick/darwin/SDL_sysjoystick_c.h
@@ -21,6 +21,7 @@
#include "../../SDL_internal.h"
#ifndef SDL_JOYSTICK_IOKIT_H
+#define SDL_JOYSTICK_IOKIT_H
#include <IOKit/hid/IOHIDLib.h>