nanotime1 is broken on windows/arm since CL 526358, which
unintentionally removed a necessary instruction. It hasn't been
noticed till now because the there is no windows/arm builder.

This CL restores the instruction.

Fixes #68996.

Change-Id: I52ef6891a3bd8e608b8538f456d181e08f93efaa
Reviewed-on: https://go-review.googlesource.com/c/go/+/607776


Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>