Build auth tests with libtool

Build auth tests with libtool

(And pthreaded.)

This was the only place consuming librokenafs directly, which is
forbidden if we are to properly support using an external roken.
Convert to libtool and throw $(LIB_roken) on at the end.

Change-Id: I0cdea690800be1022888244b613929ce3154db1d
Reviewed-on: http://gerrit.openafs.org/11476
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Tested-by: D Brashear <shadow@your-file-system.com>