amd64-windows: Fix funcall with by-pointer arguments

[Mark Kettenis]

> From: "Joel Brobecker" <brobecker@adacore.com>
> Date: Wed, 24 Oct 2012 13:23:35 -0400
> 
> Hello,
> 
> I realized a while ago that I completely misunderstood the amd64-windows
> API regarding arguments that are passed by pointer. The calling
> convention is published there:
> 
>     http://msdn.microsoft.com/en-us/library/zthk2dkh(v=vs.80).aspx

Reading that document, I think you're much much better off just
implementing your own versons of _return_value(), _push_dummy_call()
for Windows.  The complication of "classifying" the parameters makes
very little sense on Windows, and the hookds you're adding (and that
have been added in the past) only complicate the generic ABI code.