[libcxx-commits] [libcxx] feat libcxx: avoid defining std::nullptr_t in terms of ::nullptr_t (PR #73442)

[Anton Zhilin via libcxx-commits]

Anton3 wrote:

Defining an alias multiple times is allowed and does not change the behavior, as long as the definitions are the same:

```cpp
namespace std {
using nullptr_t = decltype(nullptr);
}

using nullptr_t = decltype(nullptr);
namespace std {
using ::nullptr_t;  // OK
}
```

https://github.com/llvm/llvm-project/pull/73442