SAN FRANCISCO (Reuters) - As tablets and smartphones draw more and more users away from PCs, Intel Corp is facing some difficult questions. Intel, the world's leading chipmaker, is used to being king of the personal computer market, particularly through its historic "Wintel" alliance with Microsoft Corp, which led to breathtakingly high profit margins and an 80 percent market share. But in the fast-growing and cut-throat mobile world, Intel is struggling - its market share is less than 1 percent of smartphones, trailing Qualcomm Inc, Samsung Electronics Co Ltd, ARM Holdings Plc and others. ...