Warner Bros. is facing a major setback this weekend as its latest release, the DCEU flick Birds of Prey, has failed to make an impression at the box office. Well, technically it's making an impression, but it's not the one the studio was likely hoping for. The Cathy Yan-directed film, a loose adaptation of the DC Comics Birds of Prey franchise, stars Margot Robbie, Mary Elizabeth Winstead, Jurnee Smollett-Bell, Rosie Perez, Ella Jay Basco, Ewan McGregor, and Chris Messina. All the star power plus Robbie's return as the charming hellion Harley Quinn should have gotten …