Turn off optimization for Mac Debug builds

build/common.gypi

 # Copyright 2012 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 360 matching lines @@
             'conditions': [
               ['android_full_debug==0', {
                 # Disable full debug if we want a faster v8 in a debug build.
                 # TODO(2304): pass DISABLE_DEBUG_ASSERT instead of hiding DEBUG.
                 'defines!': [
                   'DEBUG',
                 ],
               }],
             ],
           }],
+          ['OS=="mac"', {
+            'xcode_settings': {
+              'GCC_OPTIMIZATION_LEVEL': '0',  # -O0
+            },
+          }],
         ],
       },  # Debug
       'Release': {
         'variables': {
           'v8_enable_extra_checks%': 0,
         },
         'conditions': [
           ['v8_enable_extra_checks==1', {
             'defines': ['ENABLE_EXTRA_CHECKS',],
           }],
@@ skipping 53 matching lines @@
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }