runtime/race: fix test for GOMAXPROCS>1
runtime/race: fix test for GOMAXPROCS>1

Fixes issue 4530.

R=dvyukov, dave
CC=golang-dev
https://codereview.appspot.com/6933052

Committer: Dmitriy Vyukov <05e8181be3150e47da8fe2e1f18d381c75496ff4@google.com>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang