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 82a8208898f4084afdb0d731fdd14f881aac2aa3..bb57740bf0f07ff249cb92008049eee8625b60a3 100644
--- a/src/IceTargetLoweringX8632.h
+++ b/src/IceTargetLoweringX8632.h
@@ -482,8 +482,7 @@ public:
     return new TargetGlobalInitX8632(Ctx);
   }
 
-  virtual void lower(const GlobalAddress &Addr,
-                     bool DisableTranslation) override;
+  virtual void lower(const VariableDeclaration &Var) final;
 
 protected:
   TargetGlobalInitX8632(GlobalContext *Ctx);