Let benchmark runner exit with proper return codes.

tools/run_benchmarks.py

Index: tools/run_benchmarks.py
diff --git a/tools/run_benchmarks.py b/tools/run_benchmarks.py
index 42b5bf5b86892c69fad7f141975609be588245c3..1a07025f07d61a9890bfd146625e982fb8f340f0 100755
--- a/tools/run_benchmarks.py
+++ b/tools/run_benchmarks.py
@@ -345,7 +345,7 @@ def Main(args):
 
   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__), ".."))
 
@@ -395,5 +395,7 @@ def Main(args):
   else:  # pragma: no cover
     print results
 
+  return min(1, len(results.errors))
+
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(Main(sys.argv[1:]))