cmd/compile: use topo-sort in prove to correctly learn facts while walking once

cmd/compile: use topo-sort in prove to correctly learn facts while walking once

Fixes #68857

Change-Id: Ideb359cc6f1550afb4c79f02d25a00d0ae5e5c50
Reviewed-on: https://go-review.googlesource.com/c/go/+/714920
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>