Use abstract configurations to switch between opt debug settings

build/features.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 94 matching lines @@
         },
         'conditions': [
           ['v8_enable_extra_checks==1', {
             'defines': ['ENABLE_EXTRA_CHECKS',],
           }],
           ['v8_enable_handle_zapping==1', {
             'defines': ['ENABLE_HANDLE_ZAPPING',],
           }],
         ],
       },  # Debug
+      'Optdebug': {
+        'inherit_from': [ 'Debug' ],
+      },
       'Release': {
         'variables': {
           'v8_enable_extra_checks%': 0,
           'v8_enable_handle_zapping%': 1,
         },
         'conditions': [
           ['v8_enable_extra_checks==1', {
             'defines': ['ENABLE_EXTRA_CHECKS',],
           }],
           ['v8_enable_handle_zapping==1', {
             'defines': ['ENABLE_HANDLE_ZAPPING',],
           }],
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }