libafsauthent: export ktc token 'Ex' routines for Unix

libafsauthent: export ktc token 'Ex' routines for Unix

We need these to handle the modern identity structures (they are
already exported on Windows).

Reviewed-on: https://gerrit.openafs.org/13128
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 4008f83ca80c5ed7b612a13f760b4bb8b9866f2b)

Change-Id: I05d4ea37212738db6be9dace0b9cc1db1e76bd08
Reviewed-on: https://gerrit.openafs.org/13180
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Joe Gorse <jhgorse@gmail.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>