Export missing opr functions from libafsrpc

Export missing opr functions from libafsrpc

Our assertion macros expand to function calls, and we have assertions
included in macros in installed headers, so the public needs to be
able to link against them.

Export for both Unix and Windows.

Reviewed-on: https://gerrit.openafs.org/13137
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit f01ee714152a0a6247f2f456aa1f0a728d74373c)

Change-Id: I1d983d352f4838619d0b8a833e6be90207dffa87
Reviewed-on: https://gerrit.openafs.org/13193
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Joe Gorse <jhgorse@gmail.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>