works for me on trunk and CC 15.05.1
root@OpenWrt:~# opkg update
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/base/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_base.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/base/Packages.sig.
Signature check passed.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/kernel/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_kernel.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/kernel/Packages.sig.
Signature check passed.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/luci/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_luci.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/luci/Packages.sig.
Signature check passed.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/management/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_management.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/management/Packages.sig.
Signature check passed.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/packages/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_packages.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/packages/Packages.sig.
Signature check passed.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/routing/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_routing.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/routing/Packages.sig.
Signature check passed.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/telephony/Packages.gz.
Updated list of available packages in /var/opkg-lists/designated_driver_telephony.
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/telephony/Packages.sig.
Signature check passed.
root@OpenWrt:~# opkg install luafilesystem
Installing luafilesystem (1.6.2-1) to root...
Downloading http://downloads.openwrt.org/snapshots/trunk/ar71xx/generic/packages/packages/luafilesystem_1.6.2-1_ar71xx.ipk.
Configuring luafilesystem.
you can ffile the pre-compiled packe in the openwrt downloads section and load it to the temp directory of your router then install with opkg as well.
for example, for ar71xx ..
look here : https://downloads.openwrt.org/chaos_cal … ar71xx.ipk
no need to reinvent the wheel on this one 