[Bug libstdc++/62169] map iterators under _GLIBCXX_DEBUG diverge

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62169

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The standard allows iterators of different containers to be different, your
program is not portable of it assumes they will (or will not) be the same type.

I don't consider this a bug, and am not very motivated to even document it, but
will accept a documentation patch.