libdispatch: added patch to mostly work around possible crash when using NSURLSession

More info:
swiftlang/swift-corelibs-libdispatch#772

Author: triplef

Diff for: patches/libdispatch-fix-socket-closed.patch

@@ -0,0 +1,19 @@
+https://github.com/apple/swift-corelibs-libdispatch/pull/772
+---
+diff --git a/src/event/event_windows.c b/src/event/event_windows.c
+index 94674a3..148c9de 100644
+--- a/src/event/event_windows.c
++++ b/src/event/event_windows.c
+@@ -219,7 +219,11 @@ _dispatch_muxnote_disarm_events(dispatch_muxnote_t dmn,
+ 			iResult = WSAEventSelect((SOCKET)dmn->dmn_ident, NULL, 0);
+ 		}
+ 		if (iResult != 0) {
+-			DISPATCH_INTERNAL_CRASH(WSAGetLastError(), "WSAEventSelect");
++			// ignore error if socket was already closed
++			int err = WSAGetLastError();
++			if (err != WSAENOTSOCK) {
++				DISPATCH_INTERNAL_CRASH(err, "WSAEventSelect");
++			}
+ 		}
+ 		dmn->dmn_network_events = lNetworkEvents;
+ 		if (!lNetworkEvents && dmn->dmn_threadpool_wait) {