Have importlib.test use argparse instead of some hacked up solution.

Lib/importlib/test/__main__.py

@@ -4,19 +4,24 @@ Specifying the ``--builtin`` flag will run tests, where applicable, with
 builtins.__import__ instead of importlib.__import__.
 
 """
+import argparse
 from importlib.test.import_ import util
 import os.path
 from test.support import run_unittest
-import sys
 import unittest
 
 
 def test_main():
+    parser = argparse.ArgumentParser(description='Execute the importlib test '
+                                                  'suite')
+    parser.add_argument('-b', '--builtin', action='store_true', default=False,
+                        help='use builtins.__import__() instead of importlib')
+    args = parser.parse_args()
+    if args.builtin:
+        util.using___import__ = True
     start_dir = os.path.dirname(__file__)
     top_dir = os.path.dirname(os.path.dirname(start_dir))
     test_loader = unittest.TestLoader()
-    if '--builtin' in sys.argv:
-        util.using___import__ = True
     run_unittest(test_loader.discover(start_dir, top_level_dir=top_dir))