[Bug libstdc++/90682] std::terminate() will happily call a null terminate handler

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90682

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It doesn't seem appropriate to me.

If we don't want to support it we could just add __attribute__((__nonnull__))
to std::set_terminate, but I think we should support it (and so don't want it
to produce any warnings).