Fix break *FUN'address task NUM.

* ada-lex.l (task): New rule.
        * ada-lang.c (valid_task_id): Make sure the Ada task list has
        been built before using it.

gdb/ada-tasks.c

@@ -198,6 +198,7 @@ get_task_number_from_id (CORE_ADDR task_id)
 int
 valid_task_id (int task_num)
 {
+  ada_build_task_list (0);
   return (task_num > 0
           && task_num <= VEC_length (ada_task_info_s, task_list));
 }