Cleanup up git repo size

[dz333]

From @gharrma on May 24, 2018 21:20

The git repo is unnecessarily large, for historical reasons.

We can make is smaller by using Git LFS to track the large .jar files in lib outside of core git, or at least downloading them separately with a script. This would require a force push to rewrite git history so that it does not include large .jar files from past commits.

Copied from original issue: gharrma/polyllvm#56