syscall: attempt to fix windows build, supply missing constant
syscall: attempt to fix windows build, supply missing constant

R=r, brainman, rsc1
CC=golang-dev
http://codereview.appspot.com/4023043

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