[PATCH] Have 'this'-returning constructors and destructors to take advantage of the new backend 'returned' attribute

[Stephen Lin]

> Oh ok, thanks, I can do that instead. Minor issue would be that
> arrangeCXXConstructorDeclaration calls
> CGCXXABI::BuildConstructorSignature (and similarly for
> arrangeCXXDestructor), which sets the return type to the type of
> 'this', but ConstructAttributeList would then call
> CGCXXABI::HasThisReturn to determine if there's a 'this' return, so
> there'd be an implicit assumption that the two implementations are
> consistent with each other, whereas in the version I just posted
> ultimately gets the information for both from
> CGCXXABI::BuildConstructorSignature. If you're OK with that I'll go
> with that (with an assert as a consistency sanity check).

Never mind I'll fix that too.