Fix for older clang releases that lack __has_extension.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/21237002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15959 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/globals.h

@@ -116,6 +116,9 @@
 #  define V8_CC_INTEL 1  // Intel C++ also masquerades as GCC 3.2.0
 # elif defined(__clang__)
 #  define V8_CC_CLANG 1  // Clang also masquerades as GCC 4.2.1
+#  ifndef __has_extension
+#   define __has_extension __has_feature  // Compatibility with older releases
+#  endif
 # endif
 #elif defined(__ARMCC__) || defined(__CC_ARM)
 # define V8_CC_RVCT 1