I moved your post here, since the other topics are meant for supporting users that are using the official builds, so building CoreELEC yourself is off topic in those threads.
To build CoreELEC 9.2 Amlogic-ng
git clone https://github.com/CoreELEC/CoreELEC.git
cd CoreELEC
git checkout coreelec-9.2
PROJECT=Amlogic-ng ARCH=arm make image
To build CoreELEC 9.2 Amlogic
git clone https://github.com/CoreELEC/CoreELEC.git
cd CoreELEC
git checkout coreelec-9.2
PROJECT=Amlogic ARCH=arm make image
To build CoreELEC 19
git clone https://github.com/CoreELEC/CoreELEC.git
cd CoreELEC
git checkout coreelec-19
PROJECT=Amlogic-ce ARCH=arm make image