Switch GYP to use LLVM-GCC when using Xcode.

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 174 matching lines @@
           'GCC_DYNAMIC_NO_PIC': 'NO',               # No -mdynamic-no-pic
                                                     # (Equivalent to -fPIC)
           'GCC_ENABLE_CPP_EXCEPTIONS': 'NO',        # -fno-exceptions
           'GCC_ENABLE_CPP_RTTI': 'NO',              # -fno-rtti
           'GCC_ENABLE_PASCAL_STRINGS': 'NO',        # No -mpascal-strings
           # GCC_INLINES_ARE_PRIVATE_EXTERN maps to -fvisibility-inlines-hidden
           'GCC_INLINES_ARE_PRIVATE_EXTERN': 'YES',
           'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES',      # -fvisibility=hidden
           'GCC_THREADSAFE_STATICS': 'NO',           # -fno-threadsafe-statics
           'GCC_TREAT_WARNINGS_AS_ERRORS': 'YES',    # -Werror
-          'GCC_VERSION': '4.2',
+          'GCC_VERSION': 'com.apple.compilers.llvmgcc42',
           'GCC_WARN_ABOUT_MISSING_NEWLINE': 'YES',  # -Wnewline-eof
           # MACOSX_DEPLOYMENT_TARGET maps to -mmacosx-version-min
           'MACOSX_DEPLOYMENT_TARGET': '<(mac_deployment_target)',
           'PREBINDING': 'NO',                       # No -Wl,-prebind
           'SYMROOT': '<(DEPTH)/xcodebuild',
           'USE_HEADERMAP': 'NO',
           'OTHER_CFLAGS': [
             '-fno-strict-aliasing',
           ],
           'WARNING_CFLAGS': [
             '-Wall',
             '-Wendif-labels',
             '-W',
             '-Wno-unused-parameter',
             '-Wnon-virtual-dtor',
           ],
         },
         'target_conditions': [
           ['_type!="static_library"', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-search_paths_first']},
           }],
         ],  # target_conditions
       },  # target_defaults
     }],  # OS=="mac"
   ],
 }