[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 #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Thanks! This is fixed on trunk now, and will be backported to the release
branches soon.