test: adjust issue4618 for gccgo allocation behaviour
test: adjust issue4618 for gccgo allocation behaviour

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/41550044

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang