One wouldn’t necessarily think of Clint Eastwood and Eddie Murphy as vying for the same roles, but according to writer-director Walter Hill, the action-comedy classic that made Murphy a movie star began as a vehicle for the man who became famous playing Dirty Harry Callahan. “They wanted me to write it for Clint Eastwood,” Hill said of the screenplay that would ultimately become “48Hrs.” “We met with Mr. Eastwood, and he said he liked the idea, …