Yes. We have a chinese post, just updated. 【03.21更新】怎样快速编译出带glinet页面的固件 - 源代码下载 - forum.gl-inet.cn - Powered by Discuz!
It is for firmware 4.x though.

Firmware 3.x you need to use GitHub - gl-inet/imagebuilder: Warning!Please look at 'GL.iNET Imagebuilder Introduction' section. but it may not be easy to compile the same firmware.