U.S. employers stepped up hiring modestly in April, and the unemployment rate fell to 3.9 percent, evidence of the economy’s resilience amid the recent stock market chaos and anxieties about a possible trade war. Job growth amounted to a decent 164,000 last month, up from an upwardly revised 135,000 in March. The unemployment rate fell after having held at 4.1 percent for the prior six months largely because fewer people were searching for jobs. The overall unemployment rate is now the lowest since December 2000. The rate for African-Americans — 6.6 percent — is the lowest on record since 1972. Many employers say it’s difficult to find qualified workers. But they have yet to significantly bump up pay in most industries. Average hourly earnings rose 2.6 percent from a year ago. The pace of hiring has yet to be disrupted by dramatic global market swings, a recent pickup in inflation …