More Windows build fixes.

third_party/wtl/BUILD.gn

+# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+config("wtl_includes") {
+  include_dirs = [ "include" ]
+}
+
+# WTL is only header files so we use a "group" target type which doesn't
+# actually generate anything linkable, and inject the required config for
+# making the include directories work.
+group("wtl") {
+  all_dependent_configs = [ ":wtl_includes" ]
+}