Copying ensures that we respect the NTFS permissions of the parent folder.
I don't know if there is a way to tell when it is safe to simply rename.
Fixes#22343
Change-Id: I424bfe655b53b0e0fe425ce92bbc15450d52d851
Reviewed-on: https://go-review.googlesource.com/72910
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>