LONDON (Reuters) - Britain's biggest defence company BAE Systems , which counts Saudi Arabia as its third biggest customer, stuck to a forecast for flat earnings in 2018 and said programmes in the UK and the United States were making progress. BAE's update is its first since companies have come under pressure for doing business with Saudi Arabia in the wake of the killing of Saudi journalist Jamal Khashoggi in the Saudi consulate in Istanbul on Oct. 2.BAE makes 16 percent of its annual sales..