In the absence of a core dump, we do not have any information yet in the
panic output about vcl object instances, for example to find out which
object a priv belongs to when the instance address is used for
per-instance priv state.

To make this information available at the time of a panic, we add the
following:

* A struct vrt_ii (for instance info), of which a static gets
  filled in by VCC to contain the pointers to the C global variable
  instance pointers at VCC time

* A pointer to this struct from the VCL_conf to make it available to
  the varnishd worker

* dumps of the instance info for panics