cmd/compile: don't rewrite (CMP (AND x y) 0) to TEST if AND has other uses

If the AND has other uses, we end up saving an argument to the AND
in another register, so we can use it for the TEST. No point in doing that.

Change-Id: I73444a6aeddd6f55e2328ce04d77c3e6cf4a83e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/241280


Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>