Airwallex, a fintech start-up that aims to rewire clunky worldwide financial infrastructure, has swollen to US$2.6 billion in valuation, as a group of global investors joined its latest fundraising round. Investors added US$100 million to Airwallex’s Series D round, led by San Francisco-based Greenoaks Capital, which had backed Deliveroo, Discord, Stripe, Checkout.com and Brex. Grok Ventures of Australia, Skip Capital and ANZi Venture also took part in the round, taking the total money raised…