zsh: disable NIS support

The configure test for NIS and NIS+ looks for the ypcat and nisls host
utilities, respectively. This is not compatible with cross compilation.
Disable both unconditionally.

Fixes:
http://autobuild.buildroot.net/results/54c/54c9c5dff3df0a43573b03896cb0629fcae08478/
http://autobuild.buildroot.net/results/c8e/c8e30a1eb6e77ae76292b6a01bede5abb2b1b7b7/

Cc: Phil Eichinger <phil.eichinger@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/zsh/zsh.mk

@@ -9,6 +9,7 @@ ZSH_SITE = http://www.zsh.org/pub
 ZSH_SOURCE = zsh-$(ZSH_VERSION).tar.xz
 ZSH_DEPENDENCIES = ncurses
 ZSH_CONF_OPTS = --bindir=/bin
+ZSH_CONF_ENV = zsh_cv_sys_nis=no zsh_cv_sys_nis_plus=no
 ZSH_LICENSE = MIT-like
 ZSH_LICENSE_FILES = LICENCE