[Bug libstdc++/126427] New: Pair comparisons assume same types

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126427

            Bug ID: 126427
           Summary: Pair comparisons assume same types
           Product: gcc
           Version: 15.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asdfsddf1 at outlook dot com
  Target Milestone: ---

Created attachment 65138
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65138&action=edit
The compiler fails with no match for operator== of pair<long long, int> and
pair<int, long long>

According to https://en.cppreference.com/cpp/utility/pair/operator_cmp,

std::pair has comparison for different types in a pair, so logically this code
should compile:
```
#include <utility>
#include <iostream>

int main() {
    std::pair<long long, int> a{1LL, 2};
    std::pair<int, long long> b{1, 2LL};

    std::cout << (a == b); // OK, prints 1
}
```

For reference, MSVC and clang (with libc++) compiles fine with C++14, while g++
using the libstdc++ version tested does not provide the C++14 heterogeneous
std::pair comparison overloads, while other standard library implementations
do. (https://godbolt.org/z/T9efnn9zW)

I have attached the preprocessed source file just in case.