Wait on the monotonic clock to guard against changes to the system clock.

runtime/vm/vm.gypi

 # Copyright (c) 2011, 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': {
     'corelib_in_cc_file': 'corelib_in.cc',
     'corelib_cc_file': '<(SHARED_INTERMEDIATE_DIR)/corelib_gen.cc',
     'corelib_impl_in_cc_file': 'corelib_impl_in.cc',
     'corelib_impl_cc_file': '<(SHARED_INTERMEDIATE_DIR)/corelib_impl_gen.cc',
@@ skipping 13 matching lines @@
         ['exclude', '_test\\.cc|h$'],
       ],
       'include_dirs': [
         '..',
       ],
       'conditions': [
         ['OS=="linux"', {
           'link_settings': {
             'libraries': [
               '-lpthread',
+              '-lrt',
               '-lcrypto',
             ],
           },
         }],
         ['OS=="mac"', {
           'link_settings': {
             'xcode_settings': {
               'OTHER_LDFLAGS': [
                 '-lcrypto',
               ],
@@ skipping 150 matching lines @@
             '--output', '<(snapshot_test_dat_file)',
             '--input_cc', '<(snapshot_test_in_dat_file)',
             '<(snapshot_test_dart_file)',
           ],
           'message': 'Generating ''<(snapshot_test_dat_file)'' file.'
         },
       ]
     },
   ]
 }