cmd/compile/internal: intrinsify publicationBarrier on mips64x
This enables publicationBarrier to be used as an intrinsic on mips64x.
Change-Id: I4030ea65086c37ee1dcc1675d0d5d40ef8683851
Reviewed-on: https://go-review.googlesource.com/c/go/+/674855
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@golang.org>