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

[i.nixman at autistici dot org]

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

--- Comment #10 from niXman <i.nixman at autistici dot org> ---
(In reply to Jonathan Wakely from comment #9)
> There's a patch at https://gcc.gnu.org/ml/libstdc++/2017-02/msg00041.html
> 
> I haven't reviewed or tested it yet.

https://gcc.gnu.org/ml/gcc-patches/2017-03/msg00772.html

Tested on i686/x86_64-MinGW-W64 and x86_64-linux-gnu.