Add a check for GPL licenses with the libtool exception.

tools/checklicenses/checklicenses.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Makes sure that all files contain proper licensing information."""
 
 
 import optparse
 import os.path
@@ skipping 35 matching lines @@
     'BSD (4 clause)',
     'BSD-like',
 
     # TODO(phajdan.jr): Make licensecheck not print BSD-like twice.
     'BSD-like MIT/X11 (BSD like)',
 
     'BSL (v1.0)',
     # TODO(phajdan.jr): Make licensecheck not print the comma after 3.1.
     'BSL (v1.0) GPL (v3.1,)',
     'GPL (v2 or later) with Bison parser exception',
+    'GPL (v2 or later) with libtool exception',
     'GPL (v3 or later) with Bison parser exception',
     'GPL with Bison parser exception',
     'ISC',
     'LGPL',
     'LGPL (v2)',
     'LGPL (v2 or later)',
     'LGPL (v2.1)',
     'LGPL (v3 or later)',
 
     # TODO(phajdan.jr): Make licensecheck convert that comma to a dot.
@@ skipping 440 matching lines @@
   option_parser.add_option('--ignore-suppressions',
                            action='store_true',
                            default=False,
                            help='Ignore path-specific license whitelist.')
   options, args = option_parser.parse_args()
   return check_licenses(options, args)
 
 
 if '__main__' == __name__:
   sys.exit(main())