Fix Clank+Dart compilation.

runtime/vm/vm.gypi

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 {
   'variables': {
     'gen_source_dir': '<(LIB_DIR)',
     'libgen_in_cc_file': '../lib/libgen_in.cc',
     'builtin_in_cc_file': '../bin/builtin_in.cc',
     'async_cc_file': '<(gen_source_dir)/async_gen.cc',
@@ skipping 36 matching lines @@
         ['exclude', '_test\\.(cc|h)$'],
       ],
       'include_dirs': [
         '..',
       ],
       'conditions': [
         ['OS=="android"', {
           'link_settings': {
             'libraries': [
               '-lc',
-              '-lpthread',
             ],
           },
         }],
         ['OS=="linux"', {
           'link_settings': {
             'libraries': [
               '-lpthread',
               '-lrt',
             ],
           },
@@ skipping 942 matching lines @@
             '--include', 'INTENTIONALLY_LEFT_BLANK',
             '--var_name', 'INTENTIONALLY_LEFT_BLANK_TOO',
             '<(snapshot_test_dart_file)',
           ],
           'message': 'Generating ''<(snapshot_test_dat_file)'' file.'
         },
       ]
     },
   ]
 }