Disable deprecated warnings for krb5 routines

In OS X 10.9 Mavericks, Apple has marked all of the krb5 routines
as deprecated (in favor of the GSS framework).  We must disable
these warnings in order to allow the buildslave to have a successful
build.

Luckily, Apple has left in rope for us to programmatically disable
the deprecated attribute with a preprocessor macro.  Defining this
macro should be safe everywhere, so do so unconditionally.

Change-Id: Iedc920001fdc5731254336424b0ab7b27274555c
Reviewed-on: http://gerrit.openafs.org/10699
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>