cmake: fix up MESSAGE.cmake

cmake/Modules/FindZMQ.cmake

@@ -1,8 +1,19 @@
 find_path(ZMQ_INCLUDE_DIR zmq.h)
 find_library(ZMQ_LIBRARY NAMES zmq)
 
-set(ZMQ_LIBRARIES ${ZMQ_LIBRARY})
-set(ZMQ_INCLUDE_DIRS ${ZMQ_INCLUDE_DIR})
-
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(ZMQ DEFAULT_MSG ZMQ_LIBRARY ZMQ_INCLUDE_DIR)
+
+# Copy the results to the output variables and target.
+if(ZMQ_FOUND)
+  set(ZMQ_LIBRARIES ${ZMQ_LIBRARY})
+  set(ZMQ_INCLUDE_DIRS ${ZMQ_INCLUDE_DIR})
+
+  if(NOT TARGET ZMQ::ZMQ)
+    add_library(ZMQ::ZMQ UNKNOWN IMPORTED)
+    set_target_properties(ZMQ::ZMQ PROPERTIES
+      IMPORTED_LINK_INTERFACE_LANGUAGES "C"
+      IMPORTED_LOCATION "${ZMQ_LIBRARY}"
+      INTERFACE_INCLUDE_DIRECTORIES "${ZMQ_INCLUDE_DIR}")
+  endif()
+endif()