Adds tls_edit utility which patches irt_core.nexe's TLS usage.

src/trusted/validator_ragel/rdfa_validator.gyp

 # Copyright (c) 2013 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'includes': [
     '../../../build/common.gypi',
   ],
   'targets': [
     {
       'target_name': 'rdfa_validator',
       'type': 'static_library',
+      # tls_edit relies on this which is always built for the host platform.
+      'toolsets': ['host', 'target'],
       'sources': [
         'validator_features_all.c',
         'validator_features_validator.c',
         'gen/validator_x86_32.c',
         'gen/validator_x86_64.c',
       ],
     },
   ],
 }