Fix iOS build for XCode 4.6.

chrome/common/mac/objc_zombie.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "chrome/common/mac/objc_zombie.h"
 
 #include <AvailabilityMacros.h>
 
 #include <execinfo.h>
 #import <objc/runtime.h>
@@ skipping 17 matching lines @@
 
 // Deallocated objects are re-classed as |CrZombie|.  No superclass
 // because then the class would have to override many/most of the
 // inherited methods (|NSObject| is like a category magnet!).
 // Without the __attribute__, clang's -Wobjc-root-class warns on the missing
 // superclass.
 //
 //  The version of clang that ships with Xcode 4.5 does not include this
 //  warning, so it is disabled on iOS.  This may change in future Xcode
 //  releases.
-#if !defined(OS_IOS)
+//  TODO(justincohen): This is fixed in clang 4.2 in XCode 4.6.  Remove this
+//  once everyone is moved to XCode 4.6 b/7882496.
+#if !defined(OS_IOS) || \
+    (__clang_major__ > 4 || (__clang_major__ == 4 && __clang_minor__ >= 2))
 __attribute__((objc_root_class))
 #endif
 @interface CrZombie  {
   Class isa;
 }
 @end
 
 // Objects with enough space are made into "fat" zombies, which
 // directly remember which class they were until reallocated.
 @interface CrFatZombie : CrZombie {
@@ skipping 379 matching lines @@
   if (oldZombies) {
     for (size_t i = 0; i < oldCount; ++i) {
       if (oldZombies[i].object)
         object_dispose(oldZombies[i].object);
     }
     free(oldZombies);
   }
 }
 
 }  // namespace ObjcEvilDoers