Introduce the notion of function addresses in Subzero.

src/IceTargetLoweringX8632.h

Index: src/IceTargetLoweringX8632.h
diff --git a/src/IceTargetLoweringX8632.h b/src/IceTargetLoweringX8632.h
index 271d4a2fe5886681dc398e67cd948ab49f51363a..d84f4681c296c74ac827d99620cb2e5c7742afa7 100644
--- a/src/IceTargetLoweringX8632.h
+++ b/src/IceTargetLoweringX8632.h
@@ -487,8 +487,7 @@ public:
     return new TargetGlobalInitX8632(Ctx);
   }
 
-  virtual void lower(const GlobalAddress &Addr,
-                     bool DisableTranslation) override;
+  virtual void lower(const GlobalVariable &Vbl, bool DisableTranslation) final;
 
 protected:
   TargetGlobalInitX8632(GlobalContext *Ctx);