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

src/IceTargetLowering.h

Index: src/IceTargetLowering.h
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index e63ece218bed5d93ee591849b39ce60d5c486970..8620ac2f417045ae407d9d6b7c4ca680c5821414 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -206,7 +206,7 @@ public:
     RegSet_FramePointer = 1 << 3,
     RegSet_All = ~RegSet_None
   };
-  typedef uint32_t RegSetMask;
+  using RegSetMask = uint32_t;
 
   virtual llvm::SmallBitVector getRegisterSet(RegSetMask Include,
                                               RegSetMask Exclude) const = 0;