Elon Musk’s XAI Holdings is in talks with investors to raise roughly $20 billion in funding for his newly combined artificial intelligence startup and social media business, according to people familiar with the matter. If completed, the prospective deal would be the second-largest startup funding round of all time, according to data provider PitchBook, trailing only OpenAI’s $40 billion financing earlier this year. The transaction would value the company at more than $120 billion, said one of the people, all of whom asked not to be identified…