Export afs_getDirPath from shared libraries

Export afs_getDirPath from shared libraries

Add this function to the export list for libafsauthent on Windows
and Unix.

Reviewed-on: https://gerrit.openafs.org/13059
Reviewed-by: Anders Kaseorg <andersk@mit.edu>
Tested-by: Anders Kaseorg <andersk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 849ddd4fde0759e385cf3ed4054fc11c36a62fc3)

Change-Id: I39dd95185a705eaf96852e7bae9acbb5f5c50159
Reviewed-on: https://gerrit.openafs.org/13146
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>