Fix usage of SK_BUILD_* defines.

tools/skpdiff/skpdiff_main.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 // TODO(djsollen): Rename this whole package (perhaps to "SkMultiDiffer").
 // It's not just for "pdiff" (perceptual diffs)--it's a harness that allows
 // the execution of an arbitrary set of difference algorithms.
 // See http://skbug.com/2711 ('rename skpdiff')
 
 #if SK_SUPPORT_OPENCL
 
 #define __NO_STD_VECTOR // Uses cl::vectpr instead of std::vectpr
 #define __NO_STD_STRING // Uses cl::STRING_CLASS instead of std::string
-#if SK_BUILD_FOR_MAC
+#if defined(SK_BUILD_FOR_MAC)
 // Note that some macs don't have this header and it can be downloaded from the Khronos registry
 #   include <OpenCL/cl.hpp>
 #else
 #   include <CL/cl.hpp>
 #endif
 
 #endif
 
 #include "SkCommandLineFlags.h"
 #include "SkGraphics.h"
@@ skipping 229 matching lines @@
     }
 
     return 0;
 }
 
 #if !defined(SK_BUILD_FOR_IOS) && !defined(SK_BUILD_FOR_NACL)
 int main(int argc, char * argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif