bug#58524: Use ffi_prep_cif_var in pointer->procedure

[Bug reports for GUILE, GNU's Ubiquitous Extension Language]

Hi Zhu Zihao,

> It's possible to support foreign function use varargs by using
> ffi_prep_cif_var.

I'd like to use it.  Did you get it working?  Thanks!

Kind regards,
Felix Lechner