Fixed implicit function declarations by including the missing header.
diff --git a/src/core/android/SDL_android.c b/src/core/android/SDL_android.c
index f36831c..6feb48b 100644
--- a/src/core/android/SDL_android.c
+++ b/src/core/android/SDL_android.c
@@ -34,6 +34,7 @@
#include "../../video/android/SDL_androidtouch.h"
#include "../../video/android/SDL_androidvideo.h"
#include "../../video/android/SDL_androidwindow.h"
+#include "../../joystick/android/SDL_sysjoystick.h"
#include <android/log.h>
#include <pthread.h>