waf: Check for libnscd

waf: Check for libnscd

The check was in the old autoconf, but not in waf. As the code is still
in source3/lib/util_nscd.c, add the check for libnscd to allow building
and using the code.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13787

Signed-off-by: Christof Schmitt <cs@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Günther Deschner <gd@samba.org>
Autobuild-Date(master): Wed Feb 13 17:58:33 CET 2019 on sn-devel-144

(cherry picked from commit 3a793497796395ffa3efda5807bdb1ca8e09e35b)

Autobuild-User(v4-8-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-8-test): Thu Feb 21 17:42:07 CET 2019 on sn-devel-144