Mark mail/kopano/core BROKEN-sparc64

I did a bunch of poking at mail/kopano/core, but it steadfastly refuses
to build on sparc64. Mark it BROKEN-sparc64

ok?

(cc maintainer)

--Kurt

Index: Makefile
===================================================================
RCS file: /cvs/ports/mail/kopano/core/Makefile,v
retrieving revision 1.53
diff -u -p -r1.53 Makefile
--- Makefile 22 Mar 2020 11:20:34 -0000 1.53
+++ Makefile 27 Mar 2020 18:00:39 -0000
@@ -1,5 +1,7 @@
# $OpenBSD: Makefile,v 1.53 2020/03/22 11:20:34 robert Exp $

+BROKEN-sparc64= Cannot find libc with ld.lld, more library problems without lld
+
# undefined ref's to libicon*, libintl*
USE_LLD= Yes