bind99 with heimdal port requires a tweak

[Dewayne Geraghty]

Bind99 with heimdal enables GSS-TSIG, which is useful when using samba4
(or those pesky Windows Servers) in a production environment.  There is
a one line change required against
/usr/ports/dns/bind99/files/patch-configure
to avoid bind 9.9.6 bringing in heimdal base shareable libraries when
the intent is to use the heimdal port.

Please refer https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=193912

My thanks to John Marshall for his generous assistance in the hunt for a
solution.

Regards, Dewayne.