Only build runtime target on the cross compiler

tools/bots/cross-vm.py

 #!/usr/bin/python
 # Copyright (c) 2013, 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.
 
 import os
 import re
 import sys
 
 import bot
@@ skipping 24 matching lines @@
   build_py = os.path.join('tools', 'build.py')
   revision = os.environ['BUILDBOT_GOT_REVISION']
   tarball = tarball_name(arch, mode, revision)
   temporary_files = [tarball]
   bot.Clobber()
   try:
     num_run = int(os.environ['BUILDBOT_ANNOTATED_STEPS_RUN'])
     if num_run == 1:
       with bot.BuildStep('Build %s %s' % (arch, mode)):
         run([sys.executable, build_py,
-             '-m%s' % mode, '--arch=%s' % arch])
+             '-m%s' % mode, '--arch=%s' % arch, 'runtime'])
 
       with bot.BuildStep('Create build tarball'):
         run(['tar', '-cjf', tarball, '--exclude=**/obj',
              '--exclude=**/obj.host', '--exclude=**/obj.target',
              '--exclude=**/*analyzer*', 'out/', 'tools/testing/bin/'])
 
       with bot.BuildStep('Upload build tarball'):
         uri = "%s/%s" % (GCS_BUCKET, tarball)
         run([GSUTIL, 'cp', tarball, uri])
         run([GSUTIL, 'setacl', 'public-read', uri])
@@ skipping 53 matching lines @@
     mode = target_vm_pattern_match.group(2)
     target_builder(arch, mode)
   else:
     raise Exception("Unknown builder name %s" % name)
 
 if __name__ == '__main__':
   try:
     sys.exit(main())
   except OSError as e:
     sys.exit(e.errno)