[Bug libstdc++/78483] Error: reference to 'on_exit' is ambiguous

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78483

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Right, on_exit is not part of the C++ standard, so it's correct that it is not
in namespace std.