I have removed chewing gum from a number of garments, mostly inadvertantly picked up on plane/cinema seats, and my mum has used this trick for years and the white spirits has never damaged anything. Just put a little on a dry cloth, don't soak it, and rub the chewing gum. You night need to do it a few times to remove it. Wash the trousers normally straight away. Its a hell of a lot easier than freezing and scraping!