clang/win: Enable -Wmicrosoft-enum-forward-reference

remoting/host/win/BUILD.gn

 # Copyright 2016 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.
 
 import("//build/toolchain/win/midl.gni")
 import("//build/win/message_compiler.gni")
 import("//media/media_options.gni")
 import("//remoting/build/config/remoting_build.gni")
 import("//remoting/host/installer/win/generate_clsids.gni")
 
@@ skipping 97 matching lines @@
     "wts_terminal_monitor.cc",
     "wts_terminal_monitor.h",
     "wts_terminal_observer.h",
   ]
 
   configs += [
     "//build/config/compiler:wexit_time_destructors",
     "//remoting/build/config:version",
   ]
 
+  if (is_clang) {
+    # TODO(thakis): Remove this once midl.exe no longer produces nonstandard
+    # C++ (see the enums in com_imported_mstscax.tlh).
+    cflags = [ "-Wno-microsoft-enum-forward-reference" ]
+  }
+
   defines = [ "WEBRTC_CHROMIUM_BUILD" ]
 
   deps = [
     "//base:i18n",
     "//components/policy/core/common",
     "//crypto",
     "//device/power_save_blocker",
     "//ipc",
     "//remoting/base",
     "//remoting/host/security_key",
@@ skipping 370 matching lines @@
 
   output = "$root_gen_dir/remoting/{{source_name_part}}"
 
   locale_dir = webapp_locale_dir
 
   encoding = "utf-16"
 
   locales = remoting_locales
 }
 # TODO(GYP) More Windows remoting targets from remoting_host_win.gypi