Allow extern variables

gcc/elna-generic.cc

@@ -774,6 +774,7 @@ namespace elna::gcc
             {
                 DECL_INITIAL(declaration_tree) = elna_pointer_nil_node;
             }
+            DECL_EXTERNAL(declaration_tree) = declaration->is_extern;
             TREE_PUBLIC(declaration_tree) = variable_identifier.exported;
             this->current_expression = NULL_TREE;
             if (!result)