[Bug objc/77404] Add Wobjc-root-class

["vries at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77404

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #1)
> (In reply to Tom de Vries from comment #0)
> > Is the -Wobjc-root-class warning something we want to have in gcc objc as
> > well?
> 
> What's the reasoning behind clang having it?

My understanding of the reasoning is: when gcc encounters a class that does not
have a super class, either:
a. it's a new root class, or
b. the programmer forgot to specify the super class.
Given that the amount of root classes in a typical objc application is small,
the warning/attribute combination allows the trade off that by annotating the
root classes (case a) with the attribute, which should be a minor effort, we
can warn about the programmer errors (case b).