os,internal/syscall/windows: support O_* flags in Root.OpenFile
These file flags are supported by os.OpenFile since CL 699415.
Closes #73676
Change-Id: Ib37102a565f538d394d2a94bd605d6c6004f3028
Reviewed-on: https://go-review.googlesource.com/c/go/+/724621
Auto-Submit: Damien Neil <dneil@google.com> Reviewed-by: Damien Neil <dneil@google.com>
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