[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 #25 from Liu Hao <lh_mouse at 126 dot com> ---
Created attachment 44234
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44234&action=edit
test results for trunk