Improve 'make clean' to delete additional files created during make phase (CMake). Fixes ROOT-5996.

core/utils/CMakeLists.txt

@@ -35,8 +35,8 @@ add_custom_command(TARGET rootcling POST_BUILD
                    COMMAND ln -f rootcling rootcint
                    COMMAND ln -f rootcling genreflex
                    WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
-set_directory_properties(PROPERTIES ADDITIONAL_MAKE_CLEAN_FILES ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/rootcint)
-set_directory_properties(PROPERTIES ADDITIONAL_MAKE_CLEAN_FILES ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/genreflex)
+set_directory_properties(PROPERTIES ADDITIONAL_MAKE_CLEAN_FILES 
+                         "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/rootcint;${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/genreflex")
 
 install(PROGRAMS  ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/rootcint
                   ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/genreflex