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
https://golang.org/cl/4479047
1 file changed