Manufacturing in the U.S. is starting to make a comeback, and is poised for even bigger gains in the years ahead. Driven partly by more competitive labor and energy costs and companies’ desire to produce goods closer to their customers, the number of factory jobs has started to rise after plunging for decades, edging up by about 600,000 over the past four years to more than 12 million. Some U.S. companies are bringing jobs back home, and foreign businesses are setting up shop.