Macro virtual_call_varargs 

macro_rules! virtual_call_varargs {
    ($name:ident, $this:expr, $($param:expr),* $(,)?) => { ... };
    ($name:ident, $this:expr) => { ... };
}

Helper for varargs-using virtual function invocation that works with the #[vtable] attribute to support virtual calls on Windows without compiler support for the thiscall calling convention.