Rename OS(DARWIN) to OS(MACOSX).

Source/wtf/StringExtras.h

 /*
  * Copyright (C) 2006, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 13 matching lines @@
  */
 
 #ifndef WTF_StringExtras_h
 #define WTF_StringExtras_h
 
 #if OS(UNIX)
 #define HAVE_STRINGS_H 1
 #endif
 
 #if !defined(HAVE_STRNSTR)
-#if OS(DARWIN) || (OS(FREEBSD) && !defined(__GLIBC__))
+#if OS(MACOSX) || (OS(FREEBSD) && !defined(__GLIBC__))
 #define HAVE_STRNSTR 1
 #endif
 #endif
 
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
 
 #if HAVE(STRINGS_H)
 #include <strings.h>
@@ skipping 56 matching lines @@
     for (const char* start = buffer; *start && start + targetLength <= buffer + bufferLength; start++) {
         if (*start == *target && strncmp(start + 1, target + 1, targetLength - 1) == 0)
             return const_cast<char*>(start);
     }
     return 0;
 }
 
 #endif
 
 #endif // WTF_StringExtras_h