Use the pnacl-clang toolchain for (P)NaCL builds

tools/gyp/v8.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 1231 matching lines @@
         '../../src/base/utils/random-number-generator.cc',
         '../../src/base/utils/random-number-generator.h',
       ],
       'conditions': [
         ['want_separate_host_toolset==1', {
           'toolsets': ['host', 'target'],
         }, {
           'toolsets': ['target'],
         }],
         ['OS=="linux"', {
-            'link_settings': {
-              'libraries': [
-                '-lrt'
-              ]
-            },
+            'conditions': [
+              ['nacl_target_arch=="none"', {
+                'link_settings': {
+                  'libraries': [
+                    '-lrt'
+                  ],
+                },
+              }, {
+                'defines': [
+                  'V8_LIBRT_NOT_AVAILABLE=1',
+                ],
+              }],
+            ],
             'sources': [
               '../../src/base/platform/platform-linux.cc',
               '../../src/base/platform/platform-posix.cc'
             ],
           }
         ],
         ['OS=="android"', {
             'sources': [
               '../../src/base/platform/platform-posix.cc'
             ],
@@ skipping 424 matching lines @@
         }],
         ['v8_compress_startup_data=="bz2"', {
           'libraries': [
             '-lbz2',
           ]
         }],
       ],
     },
   ],
 }