go.sys: fix imports to cgc/p/go.sys, add build tags

Approach but probably not achieve a green build.

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/126120043

windows/mksyscall_windows.go

@@ -661,7 +661,7 @@ const srcTemplate = `
 package {{packagename}}
 
 import "unsafe"{{if windowsdot}}
-import "windows"{{end}}
+import "code.google.com/p/go.sys/windows"{{end}}
 
 var (
 {{template "dlls" .}}

windows/race.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build race
+// +build windows,race
 
 package windows
 

windows/race0.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !race
+// +build windows,!race
 
 package windows
 

windows/str.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build windows
+
 package windows
 
 func itoa(val int) string { // do it here rather than with fmt to avoid dependency

windows/syscall.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build windows
+
 // Package windows contains an interface to the low-level operating system
 // primitives.  OS details vary depending on the underlying system, and
 // by default, godoc will display the OS-specific documentation for the current

windows/syscall_test.go

@@ -2,11 +2,14 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build windows
+
 package windows_test
 
 import (
 	"testing"
-	"windows"
+
+	"code.google.com/p/go.sys/windows"
 )
 
 func testSetGetenv(t *testing.T, key, value string) {

windows/syscall_windows_test.go

@@ -9,7 +9,8 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
-	"windows"
+
+	"code.google.com/p/go.sys/windows"
 )
 
 func TestWin32finddata(t *testing.T) {