cmd/internal/sys: allow unaligned loads on big-endian ppc64
According to https://go.dev/wiki/MinimumRequirements, we've required
power8 since Go 1.9.
Before that, we supported power5 which couldn't do unaligned loads.
But power8 should be able to (it does for ppc64le).
In fact, I think we already support unaligned loads in some cases,
for instance cmd/compile/internal/ssa/config.go lists big-endian ppc64
as having unaligned loads.
Change-Id: I4a75f09d4b5199a889e0e8db0b3b7a1fa23145f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/631318
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Jayanth Krishnamurthy <jayanth.krishnamurthy@ibm.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>