misc/reboot: overlay $GOROOT/lib in temporary goroot
This fixes the test after CL 455357, which builds the time/tzdata file
from $GOROOT/lib/time/zoneinfo.zip.
Change-Id: I0c5afa6521b58dd3b57c3b4c3c704a622b846382
Reviewed-on: https://go-review.googlesource.com/c/go/+/462279
Run-TryBot: Ian Lance Taylor <iant@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Bypass: Ian Lance Taylor <iant@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>