Rename OS(DARWIN) to OS(MACOSX).

Source/wtf/MathExtras.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 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 31 matching lines @@
 
 const double piDouble = M_PI;
 const float piFloat = static_cast<float>(M_PI);
 
 const double piOverTwoDouble = M_PI_2;
 const float piOverTwoFloat = static_cast<float>(M_PI_2);
 
 const double piOverFourDouble = M_PI_4;
 const float piOverFourFloat = static_cast<float>(M_PI_4);
 
-#if OS(DARWIN)
+#if OS(MACOSX)
 
 // Work around a bug in the Mac OS X libc where ceil(-0.1) return +0.
 inline double wtf_ceil(double x) { return copysign(ceil(x), x); }
 
 #define ceil(x) wtf_ceil(x)
 
 #endif
 
 #if OS(OPENBSD)
 
@@ skipping 238 matching lines @@
     if (i >> 2)
         log2 += 2, i >>= 2;
     if (i >> 1)
         log2 += 1;
     return log2;
 }
 
 } // namespace WTF
 
 #endif // #ifndef WTF_MathExtras_h