Fixed an infinite loop in the block escape in analysis in ObjCARC caused by 2x blocks each assigned a value via a phi-node causing each to depend on the other.

A test case is provided as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172368 91177308-0d34-0410-b5e6-96231b3b80d8