Log Message:
Include krb5.buildlink3.mk file so that gssapi support can be built on
systems which support it (not true under NetBSD, as there is no krb5-config
file; no harm done, but a workaround should be put in place, which is
kinda laborious).

"Fixes" build under Linux (I'm not sure it was really broken, but anyway,
this was in fact a problem), as reported in PR pkg/29712.