syscall: add windows/arm64 support

types_windows_arm64.go is a copy of types_windows_amd64.go.
All that matters for these types seems to be that they are 64-bit vs 32-bit.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.

Change-Id: Ia7788d6e88e5db899371c75dc7dea7d912a689ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/288825
Trust: Russ Cox <rsc@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/syscall/types_windows_arm64.go

@@ -0,0 +1,22 @@
+// Copyright 2011 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.
+
+package syscall
+
+type WSAData struct {
+	Version      uint16
+	HighVersion  uint16
+	MaxSockets   uint16
+	MaxUdpDg     uint16
+	VendorInfo   *byte
+	Description  [WSADESCRIPTION_LEN + 1]byte
+	SystemStatus [WSASYS_STATUS_LEN + 1]byte
+}
+
+type Servent struct {
+	Name    *byte
+	Aliases **byte
+	Proto   *byte
+	Port    uint16
+}