Added DEBUG message when ObjCARC replaces a call which returns its argument...

Added DEBUG message when ObjCARC replaces a call which returns its argument verbatim with its argument to temporarily undo an optimization.

Specifically these calls return their argument verbatim, as a low-level
optimization. However, this makes high-level optimizations
harder. We undo any uses of this optimization that the front-end
emitted. We redo them later in the contract pass.

llvm-svn: 171346