Close issue25147: use C implementation of OrderedDict

Lib/enum.py

@@ -1,7 +1,12 @@
 import sys
-from collections import OrderedDict
 from types import MappingProxyType, DynamicClassAttribute
 
+try:
+    from _collections import OrderedDict
+except ImportError:
+    from collections import OrderedDict
+
+
 __all__ = ['Enum', 'IntEnum', 'unique']