By Anshuman Daga SINGAPORE (Reuters) – After years of struggling to emerge from the shadows of regional rivals, Singapore Exchange is looking to establish itself as the hub for blank-cheque firms, riding on regulatory overhaul, support by state firms, and a tech boom in its back yard. Encouraged by the flurry of Southeast Asian tech start-ups seeking funding and the bourse’s revised rules, Singapore could list up to a dozen special-purpose acquisition companies (SPACs) within the next 12-18 months, bankers, venture capitalists, and analysts say. A key test for SGX will come when such companies…