Issue #14300: Under Windows, sockets created using socket.dup() now allow overlapped I/O.

Patch by sbt.

Misc/NEWS

@@ -37,6 +37,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #14300: Under Windows, sockets created using socket.dup() now allow
+  overlapped I/O.  Patch by sbt.
+
 - Issue #13872: socket.detach() now marks the socket closed (as mirrored
   in the socket repr()).  Patch by Matt Joiner.
 

Modules/socketmodule.c

@@ -381,7 +381,7 @@ dup_socket(SOCKET handle)
         return INVALID_SOCKET;
 
     return WSASocket(FROM_PROTOCOL_INFO, FROM_PROTOCOL_INFO,
-                     FROM_PROTOCOL_INFO, &info, 0, 0);
+                     FROM_PROTOCOL_INFO, &info, 0, WSA_FLAG_OVERLAPPED);
 }
 #define SOCKETCLOSE closesocket
 #else