[Bug libstdc++/118842] `std::result_of` and `std::result_of_t` should be removed in C++20

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118842

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2025-02-12
           Keywords|                            |diagnostic
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And they will stay enabled indefinitely. We don't remove features when they're
remove from the standard, which is allowed by the standard.

There's supposed to be a -Wdeprecated-declarations warning, but it looks like I
need to move the attribute to the primary template as it doesn't work on the
partial specialization.