Fix dart-editor clobber by always clobbering all architectures if no argument is given.

tools/clean_output_directory.py

 #!/usr/bin/env python
 #
 # 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.
 #
 
 import optparse
 import shutil
 import sys
 import utils
 
 HOST_OS = utils.GuessOS()
 
 def BuildOptions():
   result = optparse.OptionParser()
   result.add_option("-m", "--mode",
       help='Build variants (comma-separated).',
       metavar='[all,debug,release]',
       default='all')
   result.add_option("--arch",
       help='Target architectures (comma-separated).',
       metavar='[all,ia32,x64,simarm,arm]',
-      default=utils.GuessArchitecture())
+      default='all')
   result.add_option("--os",
     help='Target OSs (comma-separated).',
     metavar='[all,host,android]',
     default='all')
   return result
 
 
 def ProcessOsOption(os):
   if os == 'host':
     return HOST_OS
@@ skipping 42 matching lines @@
         shutil.rmtree(build_root, ignore_errors=True)
         # On windows we have additional object files within the runtime library.
         if HOST_OS == 'win32':
           runtime_root = 'runtime/' + build_root
           print "Deleting %s" % (runtime_root)
           shutil.rmtree(runtime_root, ignore_errors=True)
   return 0
 
 if __name__ == '__main__':
   sys.exit(Main())