Use abstract configurations to switch between opt debug settings

build/toolchain.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 595 matching lines @@
                    'GCC_OPTIMIZATION_LEVEL': '0',  # -O0
                  }, {
                    'GCC_OPTIMIZATION_LEVEL': '3',  # -O3
                    'GCC_STRICT_ALIASING': 'YES',
                  }],
                ],
             },
           }],
         ],
       },  # Debug
+      'Optdebug': {
+        'inherit_from': [ 'Debug' ],
+      },
       'Release': {
         'conditions': [
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd"', {
             'cflags!': [
               '-Os',
             ],
             'cflags': [
               '-fdata-sections',
               '-ffunction-sections',
               '<(wno_array_bounds)',
@@ skipping 70 matching lines @@
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }