[Bug libstdc++/86507] New: std::filesystem not work on Windows

["tower120 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86507

            Bug ID: 86507
           Summary: std::filesystem not work on Windows
           Product: gcc
           Version: 8.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tower120 at gmail dot com
  Target Milestone: ---

Just including "filesystem" header on gcc 8.1 under windows (mingw-w64) cause
compilation error. See attached file. All 7.x with "experimental/filesystem"
worked fine.

#include <filesystem>
int main() {
    return 0;
}

Problem code here:
bits/fs_path.h

#ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
      if (__p.is_absolute()
          || (__p.has_root_name() && __p.root_name() != root_name()))
        operator=(__p);


error: no match for 'operator!=' (operand types are
'std::filesystem::__cxx11::path' and 'std::filesystem::__cxx11::path')