[Bug libstdc++/103853] std::forward_list::merge should check if __list != this

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103853

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think I can probably just add the Signed-off-by: tag based on your comment
above, and push it. But it wouldn't hurt to attach a signed-off patch here.

Thanks!