Possible defines are:
HAVE_KTH_KRB if you have the KTH Kerberos distribution (http://www.pdc.kth.se/kth-krb/)
HAVE_AFS_33A if your AFS is 3.3a or newer (Derek Atkins' LinuxAFS is currently 3.3)
HAVE_LIBKRBAFS if you have said library installed (http://andrew2.andrew.cmu.edu/dist/krbafs.html)

Note that HAVE_KTH_KRB and HAVE_LIBKRBAFS and mutually exclusive for all 
intents and purposes since they are basically the same.

Questions and comments to shadow@andrew.cmu.edu