Error compilling result.hpp on apple-clang.

Linux Compier: GCC 11
Mac Compiler: latest apple-clang

The resulting code works on linux / gcc, but on mac I get:

```
/result.hpp:3524:82: error: ISO C++ requires the name after '::~' to be found in the same scope as the name before '::~' [-Werror,-Wdtor-name]
inline RESULT_INLINE_VISIBILITY RESULT_NS_IMPL::detail::result_union::~result_union() noexcept(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
::result_union
```