Fix non-Xcode build on Mac with clang.

src/globals.h

 // 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 315 matching lines @@
 // of type F. Used to invoke generated code from within C.
 template <typename F>
 F FUNCTION_CAST(Address addr) {
   return reinterpret_cast<F>(reinterpret_cast<intptr_t>(addr));
 }
 
 
 // Compiler feature detection.
 #if defined(__clang__)
 
-// Compatibility with older clang versions.
-# ifndef __has_extension
-# define __has_extension __has_feature
-# endif
-
-# if __has_extension(cxx_override_control)
+# if __has_feature(cxx_override_control)
 #  define V8_HAVE_CXX11_FINAL
 #  define V8_HAVE_CXX11_OVERRIDE
 # endif
 
 #elif defined(__GNUC__)
 
 // g++ requires -std=c++0x or -std=gnu++0x to support C++11 functionality
 // without warnings (functionality used by the macros below).  These modes
 // are detectable by checking whether __GXX_EXPERIMENTAL_CXX0X__ is defined or,
 // more standardly, by checking whether __cplusplus has a C++11 or greater
@@ skipping 162 matching lines @@
 // the backend, so both modes are represented by the kStrictMode value.
 enum StrictModeFlag {
   kNonStrictMode,
   kStrictMode
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBALS_H_