make OpenCL optional for skpdiff

experimental/skpdiff/skpdiff_util.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.
  */
 
 #include <time.h>
 #include <dirent.h>
 #include <glob.h>
 #include "SkOSFile.h"
 #include "skpdiff_util.h"
 
+#if SK_SUPPORT_OPENCL
 const char* cl_error_to_string(cl_int err) {
     switch (err) {
         case CL_SUCCESS:                         return "CL_SUCCESS";
         case CL_DEVICE_NOT_FOUND:                return "CL_DEVICE_NOT_FOUND";
         case CL_DEVICE_NOT_AVAILABLE:            return "CL_DEVICE_NOT_AVAILABLE";
         case CL_COMPILER_NOT_AVAILABLE:          return "CL_COMPILER_NOT_AVAILABLE";
         case CL_MEM_OBJECT_ALLOCATION_FAILURE:   return "CL_MEM_OBJECT_ALLOCATION_FAILURE";
         case CL_OUT_OF_RESOURCES:                return "CL_OUT_OF_RESOURCES";
         case CL_OUT_OF_HOST_MEMORY:              return "CL_OUT_OF_HOST_MEMORY";
         case CL_PROFILING_INFO_NOT_AVAILABLE:    return "CL_PROFILING_INFO_NOT_AVAILABLE";
@@ skipping 32 matching lines @@
         case CL_INVALID_EVENT_WAIT_LIST:         return "CL_INVALID_EVENT_WAIT_LIST";
         case CL_INVALID_EVENT:                   return "CL_INVALID_EVENT";
         case CL_INVALID_OPERATION:               return "CL_INVALID_OPERATION";
         case CL_INVALID_GL_OBJECT:               return "CL_INVALID_GL_OBJECT";
         case CL_INVALID_BUFFER_SIZE:             return "CL_INVALID_BUFFER_SIZE";
         case CL_INVALID_MIP_LEVEL:               return "CL_INVALID_MIP_LEVEL";
         default:                                 return "UNKNOWN";
     }
     return "UNKNOWN";
 }
+#endif
 
 
 double get_seconds() {
     struct timespec currentTime;
     clock_gettime(CLOCK_REALTIME, &currentTime);
     return currentTime.tv_sec + (double)currentTime.tv_nsec / 1e9;
 }
 
 bool get_directory(const char path[], SkTArray<SkString>* entries) {
     // Open the directory and check for success
@@ skipping 32 matching lines @@
     char** paths = globBuffer.gl_pathv;
     while(NULL != *paths) {
         entries->push_back(SkString(*paths));
         paths++;
     }
 
     globfree(&globBuffer);
 
     return true;
 }