[Bug libstdc++/40380] class documentation should mention include file to use

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40380

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Added some more of these @headerfile annotations, but there's still more to do.