Let benchmark runner exit with proper return codes.

tools/run_benchmarks.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Performance runner for d8.
 
 Call e.g. with tools/run-benchmarks.py --arch ia32 some_suite.json
 
@@ skipping 327 matching lines @@
 
   if len(args) == 0:  # pragma: no cover
     parser.print_help()
     return 1
 
   if options.arch in ["auto", "native"]:  # pragma: no cover
     options.arch = ARCH_GUESS
 
   if not options.arch in SUPPORTED_ARCHS:  # pragma: no cover
     print "Unknown architecture %s" % options.arch
-    return False
+    return 1
 
   workspace = os.path.abspath(os.path.join(os.path.dirname(__file__), ".."))
 
   if options.buildbot:
     shell_dir = os.path.join(workspace, options.outdir, "Release")
   else:
     shell_dir = os.path.join(workspace, options.outdir,
                              "%s.release" % options.arch)
 
   results = Results()
@@ skipping 29 matching lines @@
           yield output.stdout
 
       # Let runnable iterate over all runs and handle output.
       results += runnable.Run(Runner)
 
   if options.json_test_results:
     results.WriteToFile(options.json_test_results)
   else:  # pragma: no cover
     print results
 
+  return min(1, len(results.errors))
+
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(Main(sys.argv[1:]))