Support C23's Variadics Without a Named Parameter Fixes #123773 This PR removes the static check that disallowed extern functions with ellipsis (varargs) as the only parameter since this is now valid in C23. This will not break any existing code as mentioned in the proposal document: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2975.pdf. Also, adds a doc comment for `check_decl_cvariadic_pos()` and fixes the name of the function (`varadic` -> `variadic`).