But - the repository is not "everything you need"; it actually relies on a lot from an existing platform - GCC, Lua, Make, Python etc. So, you would typically use this to cross-compile it seems.
It seems to be free now anyway, since 2005 according to the git history, under a 3-clause BSD license.
Contrary to common understanding LLVM wasn't the very first one, ACK also not, there are others predating it when diving into compiler literature.