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

[redi at gcc dot gnu.org]

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

--- Comment #23 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Nothing has been committed for gcc-8-branch so of course it isn't created.

For trunk, did you read comment 14?