American Airlines has received an offer from Qatar Airways to purchase as much as 10 percent of the Fort Worth-based carrier’s stock. American said in a regulatory filing Thursday that the bid was unsolicited, but that the CEOs of both airlines have spoken. Qatar Airways is seeking to purchase at least $808 million in shares, American Airlines has a market value of about $24 billion. Shares of American Airlines were up 5 percent in pre-market trading on Thursday.