Build a separate copy of vlib for dasalvager

Build a separate copy of vlib for dasalvager

Currently dasalvager links to vlib.a. But vlib.a is built without any
DAFS defines, and so the size of a struct DiskPartition64 is different
(since dasalvager is built with AFS_DEMAND_ATTACH_UTIL). Build our own
copies of the volume package files instead, with
AFS_DEMAND_ATTACH_UTIL defined.

(cherry picked from commit f2d067b4e48500004236b181dd5a25454f352daf)
Reviewed-on: http://gerrit.openafs.org/4875
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Change-Id: Id65a30ced198853bc6c376153671def71dd600d1
Reviewed-on: http://gerrit.openafs.org/4943
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>