Subzero: Add -Wshadow to the build.

src/IceTargetLowering.h

Index: src/IceTargetLowering.h
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index b543208d2da5d227db4bd8e3fe3964379fe7d54c..29304d7d2bb9ebd3495dee666065925f6f69db85 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -398,7 +398,7 @@ protected:
   // Perhaps there is some difference when the location is unaligned.
   static const char *getEmit32Directive() { return ".long"; }
 
-  explicit TargetDataLowering(GlobalContext *Ctx) : Ctx(Ctx) {}
+  explicit TargetDataLowering(GlobalContext *MyCtx) : Ctx(MyCtx) {}
   GlobalContext *Ctx;
 };
 
@@ -418,7 +418,7 @@ public:
   virtual void lower() {}
 
 protected:
-  explicit TargetHeaderLowering(GlobalContext *Ctx) : Ctx(Ctx) {}
+  explicit TargetHeaderLowering(GlobalContext *MyCtx) : Ctx(MyCtx) {}
   GlobalContext *Ctx;
 };