Update the existing heimdal implementation for OpenSSL 1.1.

Existing work is underway to import a newer version of heimdal, but
this patchset gets us to a fully working tree to enable more wide
spread testing of OpenSSL 1.1 for now.

I've also enabled WARNS=1 for kerberos (which is the reason for the
change in libroken). Having -Werror enabled was useful during the
1.1 updates and we probably should have warnings enabled by default
for kerberos anyway.

This passes make tinderbox, and I have also done some very light
runtime testing on amd64.

Reviewed by: bjk, jkim, emaste
Differential Revision: https://reviews.freebsd.org/D17276