Rationale:
1. It means we don't have to keep up to date https://github.com/armbian/build/blob/master/lib/general.sh#L540 with this dockerfile.
2. We also download the deps `gcc-linaro-*`
What we can do in a follow up PR is to remove the dependencies in this apt-get install, as they should be installed in `prepare_host`.
It's a file that will allow lib to run outside of its happy native debian environment, for example, on arch, or in fact... anywhere. That should actually do it, that single line. I can make it more complicated if need be, but I think that will work..... wait wait wait, have to do something about the path relativity, so..... I had it clone the repository anyway instead of just using the files that Docker will automatically copy over. May want to put this in igorpekovnik/docker to maximum cleanliness, but the idea here is that the docker image will be updated each time your repo is. It should be usable like this: docker run igorpekovnik/lib ./compile.sh
