CL 78538 was updated after running TryBots to depend on
syscall.NanoSleep which isn't available on all non-Linux platforms.

Change-Id: I1fa615232b3920453431861310c108b208628441
Reviewed-on: https://go-review.googlesource.com/79175
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>