go/build: fix windows build by commenting out references to stdout and stderr in cgotest

R=golang-dev, r, adg
CC=golang-dev
https://golang.org/cl/4561062

src/pkg/go/build/cgotest/file.go

@@ -23,8 +23,9 @@ import "unsafe"
 
 type File C.FILE
 
-var Stdout = (*File)(C.stdout)
-var Stderr = (*File)(C.stderr)
+// TODO(brainman): uncomment once stdout and stderr references are working on Windows.
+//var Stdout = (*File)(C.stdout)
+//var Stderr = (*File)(C.stderr)
 
 // Test reference to library symbol.
 // Stdout and stderr are too special to be a reliable test.