[Bug libstdc++/113386] New: std::pair comparison operators should be transparent, but are not in libstdc++

["janschultke at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113386

            Bug ID: 113386
           Summary: std::pair comparison operators should be transparent,
                    but are not in libstdc++
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: janschultke at googlemail dot com
  Target Milestone: ---

## Code to reproduce

#include <utility>

bool equals(const std::pair<int, int>& a, const std::pair<const int, const
int>& b) {
    return a == b;
}

## Explanation

Clang with -stdlib=libc++ compiles this, as does MSVC. Bug #90203 was
incorrectly closed.

std::pair comparison operators should be transparent, see
https://eel.is/c++draft/pairs.spec The standard requires the signature:

> template<class T1, class T2, class U1, class U2>
> constexpr bool operator==(const pair<T1, T2>& x, const pair<U1, U2>& y);

libstdc++ incorrectly implements this with only two template parameters:

> template<typename _T1, typename _T2>
>   inline _GLIBCXX_CONSTEXPR bool
>   operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
>   { return __x.first == __y.first && __x.second == __y.second; }