[Refactor] Use enum instead of magic number in handleX86ForceAlignArgPointerAttr, NFC

[etherzhhb]

Summary

Simple change to use Use enum instead of magic number in handleX86ForceAlignArgPointerAttr. No functional change

[echristo]

LGTM.

Let me know if you need this committed.

[etherzhhb]

Thanks, I will commit tonight. If you want this patch before that, you could commit it for me.

lib/Sema/SemaDeclAttr.cpp

static void handleX86ForceAlignArgPointerAttr(Sema &S, Decl *D,
   // Also don't warn on function pointer typedefs.
   TypedefNameDecl *TD = dyn_cast<TypedefNameDecl>(D);
   if (TD && (TD->getUnderlyingType()->isFunctionPointerType() ||
     TD->getUnderlyingType()->isFunctionType()))
     return;
   // Attribute can only be applied to function types.
   if (!isa<FunctionDecl>(D)) {
     S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
-      << Attr.getName() << /* function */0;
+      << Attr.getName() << ExpectedFunction;
     return;
   }
 
   D->addAttr(::new (S.Context)
               X86ForceAlignArgPointerAttr(Attr.getRange(), S.Context,
                                         Attr.getAttributeSpellingListIndex()));
 }