Fix -Wimplicit-fallthrough warnings (no functional change)

client/mysql.cc

@@ -1895,6 +1895,7 @@ get_one_option(int optid, const struct my_option *opt __attribute__((unused)),
     usage(1);
     status.exit_status= 0;
     mysql_end(-1);
+    break;
   case 'I':
   case '?':
     usage(0);

sql/sql_table.cc

@@ -1174,6 +1174,7 @@ static int execute_ddl_log_action(THD *thd, DDL_LOG_ENTRY *ddl_log_entry)
         action in the log entry by stepping up the phase.
       */
     }
+    /* fall through */
     case DDL_LOG_RENAME_ACTION:
     {
       error= TRUE;