fix Mac build for Xcode < 8

We need a long-term fix, but this will get 2.78 out the door.

intern/ghost/intern/GHOST_SystemCocoa.mm

@@ -285,7 +285,17 @@ extern "C" int GHOST_HACK_getFirstFile(char buf[FIRSTFILEBUFLG])
  * CocoaAppDelegate
  * ObjC object to capture applicationShouldTerminate, and send quit event
  **/
+#if defined(__clang_major__) && __clang_major__ <= 7
+/* FIXME(merwin & Juicyfruit): long-term fix for proper protocol to use
+ * merwin thinks NSApplicationDelegate is the correct protocol here. Has been around since 10.6 so we should be good... what's the problem?
+ * https://developer.apple.com/reference/appkit/nsapplicationdelegate?language=objc
+ */
+@interface CocoaAppDelegate : NSObject <NSFileManagerDelegate> {
+#else
+/* for Xcode 8 */
 @interface CocoaAppDelegate : NSObject <NSApplicationDelegate> {
+#endif
+
 	GHOST_SystemCocoa *systemCocoa;
 }
 - (void)setSystemCocoa:(GHOST_SystemCocoa *)sysCocoa;