Problem: ZMQ_HAVE_TIPC option for CMake is broken

Solution:
Fix it - there was a typo in the source list variable; it should be
'cpp-sources' and not 'cpp-source'.

CMakeLists.txt

@@ -569,7 +569,7 @@ endif (WITH_VMCI)
 
 if (ZMQ_HAVE_TIPC)
     add_definitions (-DZMQ_HAVE_TIPC)
-    list (APPEND cxx-source tipc_address.cpp tipc_connecter.cpp tipc_listener.cpp)
+    list (APPEND cxx-sources tipc_address.cpp tipc_connecter.cpp tipc_listener.cpp)
 endif (ZMQ_HAVE_TIPC)
 
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