Unbreak if libical is found at configure time since we're not bulding

http support.
breakage reported by naddy@

mail/cyrus-imapd/patches/patch-imap_sync_support_c

@@ -0,0 +1,18 @@
+$OpenBSD: patch-imap_sync_support_c,v 1.1 2017/05/29 11:56:33 ajacoutot Exp $
+
+Unbreak if libical is found at configure time since we're not building http
+support.
+
+Index: imap/sync_support.c
+--- imap/sync_support.c.orig
++++ imap/sync_support.c
+@@ -60,7 +60,9 @@
+ #include <limits.h>
+ 
+ #include "assert.h"
++#ifdef USE_CALALARMD
+ #include "caldav_alarm.h"
++#endif
+ #include "global.h"
+ #include "imap_proxy.h"
+ #include "mboxlist.h"