Use const_iterator where appropriate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105620 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/DAGDeltaAlgorithm.cpp b/lib/Support/DAGDeltaAlgorithm.cpp
index 4da3fe3..8145664 100644
--- a/lib/Support/DAGDeltaAlgorithm.cpp
+++ b/lib/Support/DAGDeltaAlgorithm.cpp
@@ -290,7 +290,7 @@
                                           const changeset_ty &Required) {
   changeset_ty Extended(Required);
   Extended.insert(Changes.begin(), Changes.end());
-  for (changeset_ty::iterator it = Changes.begin(),
+  for (changeset_ty::const_iterator it = Changes.begin(),
          ie = Changes.end(); it != ie; ++it)
     Extended.insert(pred_closure_begin(*it), pred_closure_end(*it));