Fix remaining warnings for -Wmissing-braces and enable on win clang.

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 = [
     "ia2_api_all.idl",
   ]
 }
 
 # Generate a proxy DLL from the generated code.
 shared_library("IAccessible2Proxy") {
   sources = [
     "$target_gen_dir/ia2_api_all.dlldata.c",
     "$target_gen_dir/ia2_api_all_p.c",
     "IAccessible2Proxy.def",
   ]
 
+  config("IAccessible2Proxy_warnings") {
+    if (is_clang) {
+      # MIDL generated code has a habit of omitting optional braces.
+      cflags = [ "-Wno-missing-braces" ]
+    }
+  }
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
+  configs += [ ":IAccessible2Proxy_warnings" ]
 
   defines = [ "REGISTER_PROXY_DLL" ]
 
   libs = [ "rpcrt4.lib" ]
 
   deps = [
     ":iaccessible2",
   ]
 }