Reorder relative path expansion to resolve dictionary checking issues

Modules/BuildDictionary.cmake

@@ -285,6 +285,11 @@ function(build_dictionary)
   else()
     set(BD_SOURCES_H)
   endif()
+  foreach(item IN ITEMS BD_CLASSES_H BD_CLASSES_DEF_XML linkdef_h_files)
+    if (${item})
+      cmake_path(ABSOLUTE_PATH ${item})
+    endif()
+  endforeach()
   if (BD_LIB_TARGET_VAR)
     set(${BD_LIB_TARGET_VAR} ${BD_LIB_TARGET} PARENT_SCOPE)
   endif()
@@ -417,11 +422,6 @@ function(_generate_dictionary)
   foreach(item IN LISTS BD_CLASSES_H BD_SOURCES_H)
     list(APPEND implicit_depends CXX ${item})
   endforeach()
-  foreach(item IN ITEMS BD_CLASSES_H BD_CLASSES_DEF_XML linkdef_h_files)
-    if (${item})
-      cmake_path(ABSOLUTE_PATH ${item})
-    endif()
-  endforeach()
   add_custom_command(
     # See https://gitlab.kitware.com/cmake/cmake/-/issues/21364#note_849331
     OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${BD_GENERATED_SOURCE_FILENAME} # ${AUX_OUTPUT}