tempfork/registry: add golang.org/x/sys/windows/registry + CL 236681

Temporary fork of golang.org/x/sys/windows/registry with:

   windows/registry: add Key.WaitChange wrapper around RegNotifyChangeKeyValue
   https://go-review.googlesource.com/c/sys/+/236681

tempfork/registry/export_test.go

@@ -0,0 +1,11 @@
+// Copyright 2015 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.
+
+// +build windows
+
+package registry
+
+func (k Key) SetValue(name string, valtype uint32, data []byte) error {
+	return k.setValue(name, valtype, data)
+}