unix: support TIOCGETA on GNU/Hurd

Add minimal support for GNU/Hurd to allow building third party packages
which detect terminal support.

Change-Id: Ia13fe8e9e4880e8ab062f9a2efb581320637f017
GitHub-Last-Rev: f612efbe7da35f618d1bd498a215f4b9da9c4f53
GitHub-Pull-Request: golang/sys#144
Reviewed-on: https://go-review.googlesource.com/c/sys/+/459895
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

unix/syscall_hurd_386.go

@@ -0,0 +1,29 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build 386 && hurd
+// +build 386,hurd
+
+package unix
+
+const (
+	TIOCGETA                       = 0x62251713
+)
+
+type Winsize struct {
+	Row    uint16
+	Col    uint16
+	Xpixel uint16
+	Ypixel uint16
+}
+
+type Termios struct {
+	Iflag  uint32
+	Oflag  uint32
+	Cflag  uint32
+	Lflag  uint32
+	Cc     [20]uint8
+	Ispeed int32
+	Ospeed int32
+}