[Bug libstdc++/57840] ::std ::result_of is undocumented

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57840

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Like 2371 is a comment using doxygen syntax. That comment was there in 2014
when I wrote comment 3 here.