getfsstat64 is deprecated but not yet caught by the App Store checks.
Use the supported getfsstat$INODE64 form instead to ensure forward
compatibility.

Change-Id: I0d97e8a8b254debb3de1cfcb3778dbed3702c249
Reviewed-on: https://go-review.googlesource.com/c/go/+/174200
Run-TryBot: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Keith Randall <khr@golang.org>