[Bug libstdc++/117858] [15 regression] openrct2-0.4.16 fails to build (optional:823:52: error: incomplete type ‘std::__converts_from_optional’ used in nested name specifier)

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117858

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
```
#include <optional>

struct Focus
{
    template<typename T>
    constexpr explicit Focus(T newValue, int t = 0)     {    }
};

std::optional<Focus> f;

void g()
{
  std::optional<Focus> a;
  f = a;
}

```