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.go

@@ -0,0 +1,23 @@
+// 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 hurd
+// +build hurd
+
+package unix
+
+/*
+#include <stdint.h>
+int ioctl(int, unsigned long int, uintptr_t);
+*/
+import "C"
+
+func ioctl(fd int, req uint, arg uintptr) (err error) {
+	r0, er := C.ioctl(C.int(fd), C.ulong(req), C.uintptr_t(arg))
+	if r0 == -1 && er != nil {
+		err = er
+	}
+	return
+}
+