message: Don't use POSIX on Windows
  UWP lacks POSIX compatibility. Fortunately, the CRT has similar functions.
diff: @@ -189,8 +189,13 @@ std::string reserve_unique_file_name(const std::string& path, const std::string&
  throw std::system_error(err, std::system_category());
  }
  // Remove the file so we can use the name for our own file.
  +#ifdef _WIN32
  + _close(fd);
  + _unlink(path_buffer.c_str());
  +#else
  close(fd);
  unlink(path_buffer.c_str());
  +#endif
  return path_buffer;
  }
  