clang/win: Build chromium code without -Wno-incompatible-pointer-types.

third_party/iaccessible2/BUILD.gn

 # Copyright 2014 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.
 
 assert(is_win)
 
 import("//build/toolchain/win/midl.gni")
 
 midl("iaccessible2") {
   sources = [
@@ skipping 12 matching lines @@
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
 
   defines = [ "REGISTER_PROXY_DLL" ]
 
   libs = [ "rpcrt4.lib" ]
 
   deps = [
     ":iaccessible2",
   ]
+
+  config("IAccessible2Proxy_warnings") {
+    if (is_clang) {
+      cflags = [ "-Wno-incompatible-pointer-types" ]
+    }
+  }
+  configs += [ ":IAccessible2Proxy_warnings" ]
 }