[pkg/term] temporarily use STD_*_HANDLE from syscall again

Due to the CL https://go-review.googlesource.com/c/39608/ in
x/sys/windows which changed the definitions of STD_INPUT_HANDLE,
STD_OUTPUT_HANDLE and STD_ERROR_HANDLE, we get the following failure
after re-vendoring x/sys/windows:

  07:47:01 # github.com/docker/docker/pkg/term
  07:47:01 pkg/term/term_windows.go:82: constant 4294967286 overflows int
  07:47:01 pkg/term/term_windows.go:88: constant 4294967285 overflows int
  07:47:01 pkg/term/term_windows.go:94: constant 4294967284 overflows int
  07:47:12 Build step 'Execute shell' marked build as failure

Temporarily switch back pkg/term to use these constants from the syscall
package and add a comment about it.

To really fix this, go-ansiterm should probably be switched to use
x/sys/windows.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

pkg/term/term_windows.go

@@ -6,10 +6,10 @@ import (
 	"io"
 	"os"
 	"os/signal"
+	"syscall" // used for STD_INPUT_HANDLE, STD_OUTPUT_HANDLE and STD_ERROR_HANDLE
 
 	"github.com/Azure/go-ansiterm/winterm"
 	"github.com/docker/docker/pkg/term/windows"
-	"golang.org/x/sys/windows"
 )
 
 // State holds the console mode for the terminal.
@@ -78,20 +78,24 @@ func StdStreams() (stdIn io.ReadCloser, stdOut, stdErr io.Writer) {
 		emulateStderr = false
 	}
 
+	// Temporarily use STD_INPUT_HANDLE, STD_OUTPUT_HANDLE and
+	// STD_ERROR_HANDLE from syscall rather than x/sys/windows as long as
+	// go-ansiterm hasn't switch to x/sys/windows.
+	// TODO: switch back to x/sys/windows once go-ansiterm has switched
 	if emulateStdin {
-		stdIn = windowsconsole.NewAnsiReader(windows.STD_INPUT_HANDLE)
+		stdIn = windowsconsole.NewAnsiReader(syscall.STD_INPUT_HANDLE)
 	} else {
 		stdIn = os.Stdin
 	}
 
 	if emulateStdout {
-		stdOut = windowsconsole.NewAnsiWriter(windows.STD_OUTPUT_HANDLE)
+		stdOut = windowsconsole.NewAnsiWriter(syscall.STD_OUTPUT_HANDLE)
 	} else {
 		stdOut = os.Stdout
 	}
 
 	if emulateStderr {
-		stdErr = windowsconsole.NewAnsiWriter(windows.STD_ERROR_HANDLE)
+		stdErr = windowsconsole.NewAnsiWriter(syscall.STD_ERROR_HANDLE)
 	} else {
 		stdErr = os.Stderr
 	}