[Bug libstdc++/91260] New: std::unary_function and std::binary_function still exist in C++17

[e.tadeu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91260

            Bug ID: 91260
           Summary: std::unary_function and std::binary_function still
                    exist in C++17
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: e.tadeu at gmail dot com
  Target Milestone: ---

When using -std=c++17 (or above), `unary_function` and `binary_function` should
not exist in the `std` namespace, but the following code still compiles:


    #include <functional>
    struct F : std::binary_function<int, int, int> {};