The latest Win32 checkin has changed variadic macro syntax to a more common one, but didn't add __VA_ARGS__ required by it. Turns out only WebCore uses assertion macros with multiple arguments, not JSC.
Created attachment 5522 [details] proposed patch
> Turns out only WebCore uses assertion macros with multiple arguments, not JSC. Or maybe JSC also uses them, but not with otherwise unused variables... Haven't really checked.