Fixed invalid iterators. Since the iterator is invalidated after the erase() call, we need to replace it with the new one returned. This was triggering an assert under MSVC 2012 and making all the ARCMT/ tests fail.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@163007 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ARCMigrate/ARCMT.cpp b/lib/ARCMigrate/ARCMT.cpp
index 14e13ba..9c4c2f2 100644
--- a/lib/ARCMigrate/ARCMT.cpp
+++ b/lib/ARCMigrate/ARCMT.cpp
@@ -42,7 +42,7 @@
       while (I != List.end() && I->getLevel() == DiagnosticsEngine::Note)
         ++I;
       // Clear the diagnostic and any notes following it.
-      List.erase(eraseS, I);
+      I = List.erase(eraseS, I);
       continue;
     }