Windows `stats::st_mode` and `stat` flags type.

[Lilit0x]

Synchronized the types of the st_mode property of the stat struct and the flags of the stat header file.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @JohnTitor (or someone else) some time within the next two weeks.

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[bors]

:umbrella: The latest upstream changes (presumably #3631) made this pull request unmergeable. Please resolve the merge conflicts.