Update LLDB for LLVM iterator change in r203364

What was use_iterator is now user_iterator.  Also switch to range-based
APIs, as in Clang r203365.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@203463 91177308-0d34-0410-b5e6-96231b3b80d8