libafsrpc: export more xdr functions

libafsrpc: export more xdr functions

Most of the xdr functions in the library text are to support RXAFS and
RXAFSCB RPCs, which we explicitly do not expose from libafsrpc.
As such, they do not need to be in the export list, but a couple of
generic ones probably should be exported.

Do so, for both Unix and Windows.

Reviewed-on: https://gerrit.openafs.org/13139
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 6e7db633efad1c88bb300089e3bd4c9feaea5f23)

Change-Id: I42ae33f5fdb36401d052cfb200a22aff423ac0a9
Reviewed-on: https://gerrit.openafs.org/13195
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>
Tested-by: BuildBot <buildbot@rampaginggeek.com>