os: why must Chmod mode be non-zero on Windows?

[bradfitz]

From the beginning of Go until at least Go 1.9, the os.Chmod mode parameter must be non-zero on Windows.

I don't see why, though. syscall.Chmod returns EINVAL otherwise. Can we remove that?

I documented this in CL 47254 at least.

/cc @alexbrainman @ianlancetaylor

[gopherbot]

CL https://golang.org/cl/47254 mentions this issue.

[bradfitz]

@rsc, the @golang/proposal-review NeedsDecision queries aren't working if old things like this are still open.

Bumping to Go 1.11.

[rsc]

Let's try changing this at the start of Go 1.13 and see what breaks. I can't explain it.