The star of the TV series The X-Files and Californication did his only theater work early in his career, in the small-scale “showcase” plays whose actors are lucky if they get paid enough for a taxi ride home. (He describes the shows as “Not professional. Very unprofessional.”) Now MCC Theater in New York has cast Duchovny in the lead of Neil LaBute’s new play, The Break of Noon, which opens this fall.