Makefile: introduce debugsymbols=on flag

build/standalone.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 23 matching lines @@
   'variables': {
     'component%': 'static_library',
     'clang_dir%': 'third_party/llvm-build/Release+Asserts',
     'clang_xcode%': 0,
     'visibility%': 'hidden',
     'v8_enable_backtrace%': 0,
     'v8_enable_i18n_support%': 1,
     'v8_deprecation_warnings': 1,
     'msvs_multi_core_compile%': '1',
     'mac_deployment_target%': '10.5',
+    'release_extra_cflags%': '',
     'variables': {
       'variables': {
         'variables': {
           'conditions': [
             ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or \
                OS=="netbsd" or OS=="mac" or OS=="qnx" or OS=="aix"', {
               # This handles the Unix platforms we generally deal with.
               # Anything else gets passed through, which probably won't work
               # very well; such hosts should pass an explicit target_arch
               # to gyp.
@@ skipping 135 matching lines @@
           }],
         ],
       },
       'Optdebug': {
         'inherit_from': [ 'DebugBaseCommon', 'DebugBase1' ],
       },
       'Debug': {
         # Xcode insists on this empty entry.
       },
       'Release': {
-        # Xcode insists on this empty entry.
+        'cflags+': ['<@(release_extra_cflags)'],
       },
     },
     'conditions':[
       ['(clang==1 or host_clang==1) and OS!="win"', {
         # This is here so that all files get recompiled after a clang roll and
         # when turning clang on or off.
         # (defines are passed via the command line, and build systems rebuild
         # things when their commandline changes). Nothing should ever read this
         # define.
         'defines': ['CR_CLANG_REVISION=<!(<(DEPTH)/tools/clang/scripts/update.sh --print-revision)'],
@@ skipping 373 matching lines @@
     ['use_goma==1 and ("<(GENERATOR)"=="ninja" or clang==1)', {
       'make_global_settings': [
        ['CC_wrapper', '<(gomadir)/gomacc'],
        ['CXX_wrapper', '<(gomadir)/gomacc'],
        ['CC.host_wrapper', '<(gomadir)/gomacc'],
        ['CXX.host_wrapper', '<(gomadir)/gomacc'],
       ],
     }],
   ],
 }