Convert sudo to use BSD TAILQ macros instead of home ground tail

queue functions.  This includes a private queue.h header derived
from FreeBSD.  It is simpler to just use our own header rather than
try to deal with macros that may or may not be present in various
queue.h incarnations.

plugins/sudoers/sssd.c

@@ -226,8 +226,7 @@ sudo_sss_filter_result(struct sudo_sss_handle *handle,
 }
 
 struct sudo_nss sudo_nss_sss = {
-    &sudo_nss_sss,
-    NULL,
+    { NULL, NULL },
     sudo_sss_open,
     sudo_sss_close,
     sudo_sss_parse,