make OpenCL optional for skpdiff

experimental/skpdiff/skpdiff_util.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef skpdiff_util_DEFINED
 #define skpdiff_util_DEFINED
 
-#include <CL/cl.h>
 #include "SkString.h"
 #include "SkTArray.h"
 
+#if SK_SUPPORT_OPENCL
+#include <CL/cl.h>
 /**
  * Converts an OpenCL error number into the string of its enumeration name.
  * @param  err The OpenCL error number
  * @return The string of the name of the error; "UNKOWN" if the error number is invalid
  */
 const char* cl_error_to_string(cl_int err);
+#endif
 
 /**
  * Get a positive monotonic real-time measure of the amount of seconds since some undefined epoch.
  * Maximum precision is the goal of this routine.
  * @return Amount of time in seconds since some epoch
  */
 double get_seconds();
 
 /**
  * Get file entries of the given directory.
  * @param  path    A path to a directory to enumerate
  * @param  entries A vector to return the results into
  * @return         True on success, false otherwise
  */
 bool get_directory(const char path[], SkTArray<SkString>* entries);
 
 /**
  * Gets the files that match the specified pattern in sorted order.
  * @param  globPattern The pattern to use. Patterns must be valid paths, optionally with wildcards (*)
  * @param  entries     An array to return the results into
  * @return             True on success, false otherwise
  */
 bool glob_files(const char globPattern[], SkTArray<SkString>* entries);
 
 
 #endif