VLCKit: fix compilation with Xcode 5

VLC_Prefix.pch

@@ -25,3 +25,11 @@
 #define N_(str) gettext_noop(str)
 #define gettext_noop(str) (str)
 #endif
+
+#ifndef NS_DESIGNATED_INITIALIZER
+#if __has_attribute(objc_designated_initializer)
+#define NS_DESIGNATED_INITIALIZER __attribute((objc_designated_initializer))
+#else
+#define NS_DESIGNATED_INITIALIZER
+#endif
+#endif