[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 #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jan Niklas Hasse from comment #2)
> I'm willing to help.

Great! Please read
https://gcc.gnu.org/onlinedocs/libstdc++/manual/appendix_contributing.html
especially the part about legal paperwork.

> Is there an existing starting point for Windows? Can
> boost::filesystem's implementation be used?

No. Just look at the existing code and figure out what the equivalent code
would be for Windows, and write an alternative implementation e.g. replace
calls to POSIX stat() with whatever Windows uses to query file properties, and
replace calls to POSIX chmod with whatever Windows uses to change file
permissions.