Fix unnecessary linking when using VecGeom+CUDA (#1487)

Due to missing initialization and missing an intermediary variable, dependencies found
by cuda_rdc_cuda_gather_dependencies where bleeding from one target to the next.

cmake/CudaRdcUtils.cmake

@@ -925,25 +925,31 @@ function(cuda_rdc_cuda_gather_dependencies outlist target)
   endif()
   cuda_rdc_strip_alias(target ${target})
   get_target_property(_target_type ${target} TYPE)
+  set(_deplist)
   if(NOT _target_type STREQUAL "INTERFACE_LIBRARY")
     get_target_property(_target_link_libraries ${target} LINK_LIBRARIES)
     if(_target_link_libraries)
       foreach(_lib ${_target_link_libraries})
         cuda_rdc_strip_alias(_lib ${_lib})
+        set(_libmid)
         if(TARGET ${_lib})
           cuda_rdc_get_library_middle_target(_libmid ${_lib})
         endif()
         if(TARGET ${_libmid})
-          list(APPEND ${outlist} ${_libmid})
+          list(APPEND _deplist ${_libmid})
         endif()
         # and recurse
+        set(_midlist)
+        set(_before ${_midlist})
         cuda_rdc_cuda_gather_dependencies(_midlist ${_lib})
-        list(APPEND ${outlist} ${_midlist})
+        list(APPEND _deplist ${_midlist})
       endforeach()
     endif()
   endif()
+  list(REMOVE_DUPLICATES _deplist)
+  list(APPEND ${outlist} ${_deplist})
   list(REMOVE_DUPLICATES ${outlist})
-  set_target_properties(${target} PROPERTIES CUDA_RDC_CACHED_LIB_DEPENDENCIES "${${outlist}}")
+  set_target_properties(${target} PROPERTIES CUDA_RDC_CACHED_LIB_DEPENDENCIES "${_deplist}")
   set(${outlist} ${${outlist}} PARENT_SCOPE)
 endfunction()