cmd/compile: note that some rules know the name of the opt pass
cmd/compile: note that some rules know the name of the opt pass

Change-Id: I4a70f4a52f84cf50f99939351319504b1c5dff76
Reviewed-on: https://go-review.googlesource.com/c/go/+/175777
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

nawawi/go,cloudflare/go,golang/go,nawawi/go,nawawi/go,CAFxX/go,nawawi/go,nawawi/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,golang/go,cloudflare/go,nawawi/go,akutz/go,akutz/go,golang/go,akutz/go,nawawi/go,akutz/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,cloudflare/go,cloudflare/go,cloudflare/go,golang/go,CAFxX/go,golang/go,golang/go