bpo-39481: PEP 585 for enumerate, AsyncGeneratorType, mmap (GH-19421)

diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index a5c0ae0..a1267bd 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -816,6 +816,8 @@
 #ifdef MS_WINDOWS
     {"__sizeof__",      (PyCFunction) mmap__sizeof__method,     METH_NOARGS},
 #endif
+    {"__class_getitem__",    (PyCFunction)Py_GenericAlias, METH_O|METH_CLASS,
+     PyDoc_STR("See PEP 585")},
     {NULL,         NULL}       /* sentinel */
 };