canDashC := concurrentGCBackendCompilationEnabledByDefault

	switch e := os.Getenv("GO19CONCURRENTCOMPILATION"); e {
	case "0":
		canDashC = false
	case "1":
		canDashC = true
	case "":
		// Not set. Use default.
	default:
		log.Fatalf("GO19CONCURRENTCOMPILATION must be 0, 1, or unset, got %q", e)
	}

	// TODO: Test and delete these conditions.