and to expose a handle to represent the actual case rather than having
the iterator return a reference to itself.
All of this allows the iterator to be used with common STL facilities,
standard algorithms, etc.
Doing this exposed some missing facilities in the iterator facade that
I've fixed and required some work to the actual iterator to fully
support the necessary API.
Differential Revision: https://reviews.llvm.org/D31548
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300032 91177308-0d34-0410-b5e6-96231b3b80d8
ddfada260a