DD4hep_XML_Setup: use imported XercesC target

cmake/DD4hep_XML_setup.cmake

 if(DD4HEP_USE_XERCESC)
   find_package( XercesC REQUIRED )
-  add_definitions(-DDD4HEP_USE_XERCESC)
-  include_directories(SYSTEM ${XERCESC_INCLUDE_DIRS})
-  set(XML_LIBRARIES ${XERCESC_LIBRARIES})
+  set_target_properties(XercesC::XercesC
+    PROPERTIES
+    COMPILE_DEFINITIONS DD4HEP_USE_XERCESC
+    INTERFACE_COMPILE_DEFINITIONS DD4HEP_USE_XERCESC
+    )
+  set(XML_LIBRARIES XercesC::XercesC)
 else()
   set ( DD4HEP_USE_XERCESC OFF )
   add_definitions(-DDD4HEP_USE_TINYXML)