syscall: make windows build again after d3963c0fca78 change

R=rsc, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/5373097
diff --git a/src/pkg/os/file_windows.go b/src/pkg/os/file_windows.go
index 5b09888..9462426 100644
--- a/src/pkg/os/file_windows.go
+++ b/src/pkg/os/file_windows.go
@@ -9,6 +9,7 @@
 	"runtime"
 	"sync"
 	"syscall"
+	"unicode/utf16"
 )
 
 // File represents an open file descriptor.
@@ -299,7 +300,7 @@
 // TempDir returns the default directory to use for temporary files.
 func TempDir() string {
 	const pathSep = '\\'
-	dirw := make([]uint16, MAX_PATH)
+	dirw := make([]uint16, syscall.MAX_PATH)
 	n, _ := syscall.GetTempPath(uint32(len(dirw)), &dirw[0])
 	if n > uint32(len(dirw)) {
 		dirw = make([]uint16, n)