Define Color::transparent et al. when using Clang on Windows

Source/platform/graphics/Color.cpp

 /*
  * Copyright (C) 2003, 2004, 2005, 2006, 2008 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 19 matching lines @@
 #include "wtf/Assertions.h"
 #include "wtf/HexNumber.h"
 #include "wtf/MathExtras.h"
 #include "wtf/dtoa.h"
 #include "wtf/text/StringBuilder.h"
 
 using namespace std;
 
 namespace WebCore {
 
-#if !COMPILER(MSVC)
+#if !COMPILER(MSVC) || COMPILER(CLANG)
+// FIXME: Use C++11 strong enums to avoid static data member with initializer definition problems.
 const RGBA32 Color::black;
 const RGBA32 Color::white;
 const RGBA32 Color::darkGray;
 const RGBA32 Color::gray;
 const RGBA32 Color::lightGray;
 const RGBA32 Color::transparent;
 #endif
 
 static const RGBA32 lightenedBlack = 0xFF545454;
 static const RGBA32 darkenedWhite = 0xFFABABAB;
@@ skipping 406 matching lines @@
             (color.green() * alpha  + 254) / 255,
             (color.blue() * alpha  + 254) / 255,
             alpha).rgb();
     } else
          pixelColor = color.rgb();
 
     return pixelColor;
 }
 
 } // namespace WebCore