afsio: Pass KRB5_LDFLAGS along with KRB5_LIBS

We need this in case e.g. the krb5 library we're using is in an
alternate location, so we can pass -L. aklog already does this, so do
it for afsio, too.

This is a 1.6-only change. On master, this problem went away when the
krb5 ldflags/cflags/etc were standardized in commit
6f9443e702745d1e371eb72ad7fcba5cac47f3db.

Thanks to Måns Nilsson for reporting this.

Change-Id: I79aeb1f4de123b7550b64c1890a2773a44ff8d1e
Reviewed-on: http://gerrit.openafs.org/9692
Reviewed-by: Simon Wilkinson <simonxwilkinson@gmail.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>