os, syscall: permit setting mtime to Unix 0 on Windows
This edge case was accidentally broken by CL 219638.
Change-Id: I673b3b580fbe379a04f8650cf5969fe9bce83691
Reviewed-on: https://go-review.googlesource.com/c/go/+/495036 Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>