Thirty years after its initial Broadway run, Scottish actor Ewan McGregor is heading an all-star cast in the latest revival of Tom Stoppard’s Tony winning play, “The Real Thing,” about love, truth, marriage and infidelity. The Roundabout Theatre Company production, which opened on Thursday, marks the Broadway debut of McGregor, known for his film roles in “The Impossible” and “Moulin Rouge” and his co-star Maggie Gyllenhaal. The pair play lovers in roles originated on Broadway by Jeremy Irons and Glenn Close in the 1984 production directed by Mike Nichols.