Ah, I understand. so, a couple of things to consider.
First, some of the headers in krb5-multidev aregenerated and are not guaranteed to be the same between the host and build. So, the official interface is that you had better use the right krb5-multidev or you might be very sad. In practice, I think it will generlaly work okay on the Debian architectures if you mix and match, but no guarantees. Secondly, upstream's position is people should use pkgconfig and that krb5-config is a legacy interface that is semi-deprecated. So, I understand your options now, and think that exporting CC is a fine solution for this case, but preferring pkgconfig to changing krb5-config is what upstream and I would recommend.
