Meryl Streep always claims she can’t be bothered with fashion. “I just found it so exhausting,” she told W magazine after working on “The Devil Wears Prada.” “Which bag? Which shoes? Which ring? Which earrings? How does it all look?” But lately she’s given her fans cause to wonder if she was just acting. At the London premiere of “Mamma Mia” on Monday, the Oscar winner showed no signs of accessories fatigue, embellishing her Donna Karan evening trenchcoat with a chic triple-strap belt, playful peep-toe pumps and movie star-worthy sunglasses. It was as glam as she’s ever looked, and surely her fellow premiere goers, Tom Ford and Valentino, could appreciate the effort. But if Streep is as unfazed by fashion as she says she is, let’s just hope that when she ran into the two designers, she at least acted interested.