I've heard good things about "LLVM Techniques, Tips, and Best Practices" [0] but haven't gotten around to reading it myself yet. Packt does not always have the best reputation but it was recommended to me by someone I know and the reviews are also solid, so mentioning in case it's at all helpful.

0: https://www.packtpub.com/en-us/product/llvm-techniques-tips-...