[Bug libstdc++/78870] Support std::filesystem on Windows

[lh_mouse at 126 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78870

--- Comment #24 from Liu Hao <lh_mouse at 126 dot com> ---
(In reply to Jonathan Wakely from comment #23)
> Nothing has been committed for gcc-8-branch so of course it isn't created.
> 
> For trunk, did you read comment 14?

Sorry didn't notice it. I started a new build just now.