For decades, U.S.-based studios have assembled international blockbusters by formula, using well-worn plots and calculated casting to fetch global audiences.The budgets of these would-be megahits are astronomical, and comparable amounts are spent on the films’ marketing and publicity as well.“The Great Wall,” which was produced for the modest-under-the-circumstances sum of $150 million, is the most expensive film ever made in China.Director Yimou Zhang (“House of Flying Daggers”) and almost …