cmd/compile: Install testcases for flag constant Ops

cmd/compile: Install testcases for flag constant Ops

Flag constant Ops on arm and arm64 are under refactoring, this change adds
a couple of testcases that verify the behavior of 'noov' branches.

Updates #39505
Updates #38740
Updates #39303
Change-Id: I493344b52276900cd296c32da494d72932dfc9be
Reviewed-on: https://go-review.googlesource.com/c/go/+/238677
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>