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

[pinskia at gcc dot gnu.org]

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

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is most likely because _GNU_SOURCE is defined when compiling with C++ code
in GNU C++ mode.