Linux: fix build with system libevent.

third_party/libevent/libevent.gyp

 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'use_system_libevent%': 0,
   },
   'conditions': [
     ['use_system_libevent==0', {
@@ skipping 48 matching lines @@
               'include_dirs': [ 'solaris' ]
             }],
           ],
         },
       ],
     }, {  # use_system_libevent != 0
       'targets': [
         {
           'target_name': 'libevent',
           'type': 'settings',
+          'toolsets': ['host', 'target'],
           'direct_dependent_settings': {
             'defines': [
               'USE_SYSTEM_LIBEVENT',
             ],
           },
           'link_settings': {
             'libraries': [
               '-levent',
             ],
           },
         }
       ],
     }],
   ],
 }