Consumed Analysis: Allow parameters that are passed by non-const reference
to be treated as return values, and marked with the "returned_typestate"
attribute.  Patch by chris.wailes@gmail.com; reviewed by delesley@google.com.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192932 91177308-0d34-0410-b5e6-96231b3b80d8