syscall: fix Windows Signalled
syscall: fix Windows Signalled

Thanks to fhs.

R=golang-dev, r2
CC=ality, fhs, golang-dev
http://codereview.appspot.com/4375044

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