internal/runtime/maps: loop invariant code motion with h2(hash) by hand

internal/runtime/maps: loop invariant code motion with h2(hash) by hand

Change-Id: I0cd9763aeedfe326bc566da39b8be0d0ebd113ec
GitHub-Last-Rev: 1ec88644148deb41eea2ae89f7f1fb1759b37c27
GitHub-Pull-Request: golang/go#74952
Reviewed-on: https://go-review.googlesource.com/c/go/+/694016
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>