wingui: fix Makefile after rename

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/4477046

src/pkg/exp/wingui/Makefile

@@ -18,7 +18,7 @@ GOFILES=\
 include ../../../Make.cmd
 
 zwinapi.go: winapi.go
-	$(GOROOT)/src/pkg/syscall/mksyscall_windows.sh $< \
+	$(GOROOT)/src/pkg/syscall/mksyscall_windows.pl $< \
 		| sed 's/^package.*syscall$$/package main/' \
 		| sed '/^import/a \
 			import "syscall"' \

src/pkg/exp/wingui/zwinapi.go

-// mksyscall_windows.sh winapi.go
+// mksyscall_windows.pl winapi.go
 // MACHINE GENERATED BY THE COMMAND ABOVE; DO NOT EDIT
 
 package main