cmd/compile/internal/gc: simplify bool expression
cmd/compile/internal/gc: simplify bool expression

Change-Id: Idcd79788e64947a927af662b6394ac7218e62ba8
Reviewed-on: https://go-review.googlesource.com/135836
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

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