runtime: unify ppc64/ppc64le library entry point

runtime: unify ppc64/ppc64le library entry point

Cq-Include-Trybots: luci.golang.try:gotip-linux-ppc64le_power10
Change-Id: Ifd7861488b1b47a5d30163552b51838f2bef7248
Reviewed-on: https://go-review.googlesource.com/c/go/+/706395
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>