WASHINGTON—U.S. employers posted a record-high number of open jobs for the second straight month as a rapidly rebounding economy generates intense demand for workers. The number of available jobs on the last day of May rose slightly to 9.21 million, from 9.19 million in April, the Labor Department said Wednesday. That is the highest since records began in December 2000. The previously reported figure for April of 9.3 million was revised lower. The number of people quitting their jobs slipped in May from a record high in April, but remains elevated. And the percentage of workers getting laid off hit a record low in May, the report said. The figures point to a tight job market, with employers forced to pay more to attract workers yet still struggling to fill open jobs. And many workers are leaving jobs for better-paying positions at other companies. It’s unusual for such dynamics to …