syscall: fix bug in mksyscall_windows.pl
syscall: fix bug in mksyscall_windows.pl

This change fixes generation of "shadow" variables for bool parameters.
Before the change, it was naming all bool variables with the same name of _p0.
Now it calls them _p0, _p1, ... So the code could compile.

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/4479047

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