std::format_kind failing with gcc-16 (trunk)

[steve-downey]

It looks like gcc-16 now advertises support for range formatting, and the static_assert check is failing. I don't see an obvious error with the definition of the template variable for std::format_kind.

It also looks like this could have been checked in gcc-15. The feature test macros trail behind the library support.

[steve-downey]

At least part of the problem is that we're checking

#if defined(__cpp_lib_format_ranges)

without including <version>

https://github.com/bemanproject/optional/blob/main/include/beman/optional/optional.hpp#L9-L11

It's not a compiler intrinsic.

[steve-downey]

std::format_kind was added to gcc-15 post 15.1.0. Can reproduce on the compiler release branch as well as with gcc-16 (trunk)

[steve-downey]

Fixed by #124