Magnanimous Michael Douglas has offered his support to his frail old friend Kathleen Turner, who’s suffering from an advanced case of rheumatoid arthritis. Despite their adversarial relationships onscreen, the former co-stars, who headlined the ’80s blockbusters Romancing the Stone, The Jewel of the Nile and The War of the Roses, have been close pals for 40-plus years. Douglas, 80, wants Turner, 70, to know he’s there for her, sources told RadarOnline.com. “He worries about her. Even though she’s still feisty as ever mentally, it appears her illness has taken a turn for the worse.” Kathleen wa…