New ObjC warning: circular containers.

New ObjC warning: circular containers.

This commit adds new warning to prevent user from creating 'circular containers'.

Mutable collections from NSFoundation allows user to add collection to itself, e.g.:

NSMutableArray *a = [NSMutableArray new];
[a addObject:a];

The code above leads to really weird behaviour (crashes, 'endless' recursion) and
retain cycles (collection retains itself) if ARC enabled.

Patch checks the following collections:
  - NSMutableArray,
  - NSMutableDictionary,
  - NSMutableSet,
  - NSMutableOrderedSet,
  - NSCountedSet.

llvm-svn: 231265