Remove v8 source dependency, enable more compiler warnings

dart/tools/gyp/configurations_xcode.gypi

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # The purpose of this file and others in this directory is to simulate
 # the Chromium build enviroment. This file is included in all GYP
-# files that are used by the Dart project. This includes V8's GYP
-# files.
+# files that are used by the Dart project.
 
 # READ BEFORE EDITING:
 # Do not add Dart VM specific configuration to this file. Instead,
 # modify runtime/tools/gyp/runtime-configurations.gypi.
 
 {
   'variables': {
     'xcode_gcc_version%': '<!(python <(DEPTH)/tools/gyp/find_mac_gcc_version.py)',
   },
   'target_defaults': {
@@ skipping 31 matching lines @@
           'GCC_CW_ASM_SYNTAX': 'NO', # Remove -fasm-blocks.
 
           'GCC_ENABLE_PASCAL_STRINGS': 'NO',
           'GCC_ENABLE_TRIGRAPHS': 'NO',
           'COMBINE_HIDPI_IMAGES': 'YES',
         },
       },
     },
   },
 }