check for error_message

check for error_message

IRIX apparently has enough krb5 to try building aklog, but no
error_message. ok. so let's cope

Reviewed-on: http://gerrit.openafs.org/3208
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 572f9baaeb626293f4db62a66db1ea9b9a373c03)

Change-Id: I44c71ffedcbe55db696db667d1941a7bdc781cff
Reviewed-on: http://gerrit.openafs.org/3987
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>