turn on libc++ for iOS

gyp/common_conditions.gypi

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
@@ skipping 541 matching lines @@
           },
         },
         'xcode_settings': {
           'ARCHS': ['armv7'],
           'CODE_SIGNING_REQUIRED': 'NO',
           'IPHONEOS_DEPLOYMENT_TARGET': '<(ios_sdk_version)',
           'SDKROOT': 'iphoneos',
           'TARGETED_DEVICE_FAMILY': '1,2',
           'OTHER_CPLUSPLUSFLAGS': [
             '-std=c++0x',
+            '-stdlib=libc++',
             '-fvisibility=hidden',
             '-fvisibility-inlines-hidden',
           ],
           'GCC_THUMB_SUPPORT': 'NO',
         },
       },
     ],
 
     [ 'skia_os == "android"',
       {
@@ skipping 66 matching lines @@
           'LD_RUNPATH_SEARCH_PATHS': ['@executable_path/.'],
       },
     }],
 
   ], # end 'conditions'
   # The Xcode SYMROOT must be at the root. See build/common.gypi in chromium for more details
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }