cmd/compile: use MOVBE instruction for GOAMD64>=v3

cmd/compile: use MOVBE instruction for GOAMD64>=v3

In CL 354670, I copied some existing rules for convenience but forgot
to update the last rule which broke `GOAMD64=v3 ./make.bat`

Revive CL 354670

Change-Id: Ic1e2047c603f0122482a4b293ce1ef74d806c019
Reviewed-on: https://go-review.googlesource.com/c/go/+/356810
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>