Enable whole-program virtual function optimization in LTO mode.

tools/mb/mb_config.pyl

 # Copyright 2015 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.
 
 {
   # This is a map of buildbot master names -> buildbot builder names ->
   # config names (where each config name is a key in the 'configs' dict,
   # below). MB uses this dict to look up which config to use for a given bot.
   'masters': {
     # Take care when changing any of these builders to ensure that you do not
@@ skipping 1779 matching lines @@
     'libfuzzer': { 'gn_args': 'use_libfuzzer=true' },
 
     'ubsan_security': { 'gn_args': 'is_ubsan_security=true' },
 
     'lsan': {
       'gn_args': 'is_lsan=true',
       'gyp_defines': 'lsan=1',
     },
 
     'lto': {
-       'gn_args': 'is_lto=true',
+       'gn_args': 'allow_posix_link_time_opt=true',
        'gyp_defines': 'use_lto=1',
      },
 
     'mac_strip': {
       'gn_args': 'error', # TODO(GYP): Port mac_strip_release
       'gyp_defines': 'mac_strip_release=1',
     },
 
     'minimal_symbols': {
       'gn_args': 'symbol_level=1',
@@ skipping 112 matching lines @@
       'gn_args': 'is_component_build=true enable_iterator_debugging=false',
       'gyp_defines': 'component=shared_library build_for_tool=drmemory',
     },
 
     'valgrind': {
       # TODO: add gn_args for 'build_for_tool=memcheck'
       'gyp_defines': 'build_for_tool=memcheck',
     }
   },
 }