Cemex exercised about 136 million stock options on Monday, as part of its executive compensation program.    Cemex, the world’s third largest cement producer, exercised the options as part of a "long-term variable compensation program" for executives, in which new 7.5 year options were also given to the high-level employees.    The options on Monday were exercised at 78.35 pesos per share, and the newly issued options carry a strike price that is the equivalent of $0.50 higher, increasing by 5.5 percent every year.