Use IoctlSetPointerInt from golang.org/x/sys/unix

Use unix.IoctlSetPointerInt instead of manually implementing it. This
fixes the build on darwin where direct syscalls, i.e.
unix.Syscall(SYS_IOCTL, ...) are no longer allowed and exported as of
golang/sys@6fcdbc0

tc_darwin.go

@@ -19,7 +19,6 @@ package console
 import (
 	"fmt"
 	"os"
-	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
@@ -29,18 +28,10 @@ const (
 	cmdTcSet = unix.TIOCSETA
 )
 
-func ioctl(fd, flag, data uintptr) error {
-	if _, _, err := unix.Syscall(unix.SYS_IOCTL, fd, flag, data); err != 0 {
-		return err
-	}
-	return nil
-}
-
 // unlockpt unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by f.
 // unlockpt should be called before opening the slave side of a pty.
 func unlockpt(f *os.File) error {
-	var u int32
-	return ioctl(f.Fd(), unix.TIOCPTYUNLK, uintptr(unsafe.Pointer(&u)))
+	return unix.IoctlSetPointerInt(int(f.Fd()), unix.TIOCPTYUNLK, 0)
 }
 
 // ptsname retrieves the name of the first available pts for the given master.