exp/wingui: remove reference to Make.inc

R=golang-dev, bradfitz, alex.brainman
CC=golang-dev
https://golang.org/cl/5757058

src/pkg/exp/wingui/Makefile

@@ -2,23 +2,8 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-GOOS=windows
-
-include ../../../Make.inc
-
-LD:=$(LD) -Hwindowsgui
-
-TARG=wingui
-
-GOFILES=\
-	gui.go\
-	winapi.go\
-	zwinapi.go\
-
-include ../../../Make.cmd
-
 zwinapi.go: winapi.go
 	(echo '// +build windows'; \
-	$(GOROOT)/src/pkg/syscall/mksyscall_windows.pl $<) \
+	../../syscall/mksyscall_windows.pl $<) \
 		| gofmt \
 		> $@