According to your other's thread: Telegram on Galileo (prob) you are using the IoT image is this right? Or now are you using the SD image?
If you are using the SD image you need to install git in your board.
If you are using the IoT image and you run git --version you should get: git version 1.9.0
Have you try to use: git clone --recursive git://github.com/vysheng/tg.git && cd tg What is the outcome of it?
I am using IOT image and I checked for git version I have "git version 1.9.0"
When I execute "git clone --recursive git://github.com/vysheng/tg.git && cd tg "
I got same error "submodule is not git command"
when i gone for ./configure and make its not work meas again I am facing same problem that is git