I think people have made the point with specific references like "coup d'etat" and "faux pas". I think the general answer is that language standards are fluid and common usage tends to become standard over time. The word "croissant" might be in a transition period depending on personal experience. I've always heard it in pronounced in the French or at least French-ish way, so to me "croy-sant" sounds kind of hillbilly. I grew up with Pillsbury Crescent Rolls.