make SDL_syswm.h work with apple's older gcc versions

c.f. https://bugzilla.libsdl.org/show_bug.cgi?id=2694

include/SDL_syswm.h

@@ -256,8 +256,12 @@ struct SDL_SysWMinfo
 #if defined(SDL_VIDEO_DRIVER_COCOA)
         struct
         {
-#if defined(__OBJC__) && defined(__has_feature) && __has_feature(objc_arc)
+#if defined(__OBJC__) && defined(__has_feature)
+        #if __has_feature(objc_arc)
             NSWindow __unsafe_unretained *window; /**< The Cocoa window */
+        #else
+            NSWindow *window;                     /**< The Cocoa window */
+        #endif
 #else
             NSWindow *window;                     /**< The Cocoa window */
 #endif
@@ -266,8 +270,12 @@ struct SDL_SysWMinfo
 #if defined(SDL_VIDEO_DRIVER_UIKIT)
         struct
         {
-#if defined(__OBJC__) && defined(__has_feature) && __has_feature(objc_arc)
+#if defined(__OBJC__) && defined(__has_feature)
+        #if __has_feature(objc_arc)
             UIWindow __unsafe_unretained *window; /**< The UIKit window */
+        #else
+            UIWindow *window;                     /**< The UIKit window */
+        #endif
 #else
             UIWindow *window;                     /**< The UIKit window */
 #endif