First get LXC going: http://goran.krampe.se/2017/10/24/nim-crash-course-inside-lxc/
When you got LXC running, then create a machine and log into it:
lxc launch ubuntu:18.04 orx
lxc exec orx -- su --login ubuntu
Then inside Ubuntu:
# Freshen up
sudo apt update && sudo apt upgrade
# Install tools needed to build
sudo apt-get install gcc make git unzip wget xz-utils libsdl2-dev libsdl2-mixer-dev libfreeimage-dev libfreetype6-dev libcurl4-openssl-dev rapidjson-dev libasound2-dev libgl1-mesa-dev build-essential libboost-all-dev cmake fonts-droid-fallback libvlc-dev libvlccore-dev vlc-bin texinfo premake4 golang
# Clone EmuELEC with ORX in it
git clone https://github.com/gokr/EmuELEC.git
# Build ORX for ARM in EmuELEC (will take a lot of time since it first builds tons of dependencies)
cd EmuELEC
PROJECT=Amlogic ARCH=arm DISTRO=EmuELEC scripts/build orx