Refactor all instances of `typedef y x` to the C++11 `using x = y` syntax.

src/IceCfg.h

Index: src/IceCfg.h
diff --git a/src/IceCfg.h b/src/IceCfg.h
index 3c8972df6ad80f58b1b22035a38636aff4a2fe6f..78fd47aa28c5f0cb75d7128468d54b90d6fb0af2 100644
--- a/src/IceCfg.h
+++ b/src/IceCfg.h
@@ -96,7 +96,7 @@ public:
   void swapNodes(NodeList &NewNodes);
   /// @}
 
-  typedef int32_t IdentifierIndexType;
+  using IdentifierIndexType = int32_t;
   /// Adds a name to the list and returns its index, suitable for the
   /// argument to getIdentifierName().  No checking for duplicates is
   /// done.  This is generally used for node names and variable names