pam: Build using libtool

Build the pam_afs and pam_afs.krb modules using libtool, so they
fit in with the rest of the new build infrastructure.

This requires some additonal symbol exports from auth and kauth,
which are included

Change-Id: I97a130ba69216cd63ba388f2aaabe830a0c4543f
Reviewed-on: http://gerrit.openafs.org/8900
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>