Do not dereference std::unique_ptr by default

Summary:
Displaying the object pointed by the unique_ptr can cause an infinite
recursion when we have a pointer loop so this change stops that
behavior. Additionally it makes the unique_ptr act more like a class
containing a pointer (what is the underlying truth) instead of some
"magic" class.

Reviewers: labath, jingham

Differential Revision: https://reviews.llvm.org/D31366

llvm-svn: 299249