[C++11] Update Clang for the change to LLVM's Use-Def chain iterators in

[C++11] Update Clang for the change to LLVM's Use-Def chain iterators in
r203364: what was use_iterator is now user_iterator, and there is
a use_iterator for directly iterating over the uses.

This also switches to use the range-based APIs where appropriate.

llvm-svn: 203365