ds-nslookup is a small, self-contained and dead-simple implementation of the non-interactive mode of nslookup.
It's very limited and should be used only as a replacement for the busybox nslookup.
It uses the functions provided by libresolv to send DNS queries to a local or a remote nameserver.
$ cd ds-nslookup
$ make
$ make install
Tested under Arch Linux x86_64 and openwrt mips 24k.
To integrate this package in OpenWRT you should make a symlink to openwrt/packages. Then you can select the package in the Network Section of menuconfig:
$ cd $OPENWRT
$ mkdir package/ds-nslookup
$ ln -sf $NSPATH/openwrt/Makefile package/ds-nslookup
$ make menuconfig
where NSPATH is the path to ds-nslookup and OPENWRT is the path to openwrt sources.