Wall Street bankers may be salivating at the upcoming flotation of Arm Holdings, the British company whose chip designs help power most of the world’s smartphones. Yet even though Arm has become the world’s dominant provider of a nearly indispensable product, it has a clear Achilles’ heel: its relationship with China. With so-called ‘cornerstone’ investors including Apple, Google and Nvidia already signed up, Arm this week said it is aiming for a market capitalization of up to $52 b