[C++11] Add 'override' keyword to virtual methods that override their base class.

llvm-svn: 203746
diff --git a/clang/lib/Serialization/GlobalModuleIndex.cpp b/clang/lib/Serialization/GlobalModuleIndex.cpp
index 5cd3ad5..b9e6130 100644
--- a/clang/lib/Serialization/GlobalModuleIndex.cpp
+++ b/clang/lib/Serialization/GlobalModuleIndex.cpp
@@ -835,7 +835,7 @@
       End = Idx.key_end();
     }
 
-    virtual StringRef Next() {
+    StringRef Next() override {
       if (Current == End)
         return StringRef();