[Bug libstdc++/88151] Define iterator_traits::* for output iterators to actual values when possible (rather than to void)

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88151

--- Comment #1 from Antony Polukhin <antoshkka at gmail dot com> ---
The implementation is quite trivial:
https://gist.github.com/zmij/329005f5d06369243988ef6301f37616