I don't think there's much value in adding an Annex K comparison anywhere since none of the compared libcs have Annex K functions; comparison items are only meaningful where they differ. Even if some libcs did have it, though, I'd be hesitant to put it under hardening. My concept of "hardening" is providing additional properties beyond the scope of the specification (usually this means in places where undefined behavior occurs, but it could also be implementation-defined things, such as using an alternate pointer representation that allows as much bounds-checking as C makes possible).
