[Webrtc] Reenable libc++ on ubsan

tools_webrtc/mb/mb_config.pyl

 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # FOR DETAILS ON THIS FILE SEE THE MAIN COPY IN //tools/mb/mb_config.pyl.
 # This is configuration for standalone WebRTC bots. It is used to keep the bot
@@ skipping 210 matching lines @@
     'msan_clang_release_bot_x64': [
       'gn', 'msan', 'clang', 'openh264_release_bot', 'x64'
     ],
     'tsan_clang_release_bot_x64': [
       'gn', 'tsan', 'clang', 'openh264_release_bot', 'x64'
     ],
     'ubsan_clang_release_bot_x64': [
       'gn', 'ubsan', 'clang', 'openh264_release_bot', 'x64'
     ],
     'ubsan_vptr_clang_release_bot_x64': [
-      'gn', 'ubsan_vptr', 'clang', 'openh264_release_bot', 'x64',
-      'use_default_libcxx'
+      'gn', 'ubsan_vptr', 'clang', 'openh264_release_bot', 'x64'
     ],
     'debug_bot_x86': [
       'gn', 'openh264_debug_bot', 'x86'
     ],
     'release_bot_x86': [
       'gn', 'openh264_release_bot', 'x86'
     ],
     'debug_bot_x64': [
       'gn', 'openh264_debug_bot', 'x64'
     ],
@@ skipping 229 matching lines @@
 
     'x86': {
       'gn_args': 'target_cpu="x86"',
     },
 
     'use_default_libcxx': {
       'gn_args': 'use_custom_libcxx=false',
     }
   },
 }