[libcxx-commits] [libcxx] [libc++] fix `flat_set`'s transparent `insert` (PR #133402)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Actually, it looks like we have the following behavior: https://godbolt.org/z/14n91xqdj

```
using T = char;

void f(T (&a1)[3], T (&a2)[3]) {
    a1 < a2;
}
```

- GCC 14: accepts code
- GCC trunk: rejects with error
- Clang 19: accepts code with a warning
- Clang trunk: rejects with error

I think the errors only happen in C++26 mode. In C++23 we get warnings at most in all cases.

https://github.com/llvm/llvm-project/pull/133402