cmd/compile: move s390x over to new bounds check strategy

cmd/compile: move s390x over to new bounds check strategy

Change-Id: I86ed1a60165b729bb88a8a418da0ea1b59b3dc10
Reviewed-on: https://go-review.googlesource.com/c/go/+/682499
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Munday <mikemndy@gmail.com>
Reviewed-by: Mark Freeman <mark@golang.org>