Add PGO support

If you want to try to achieve even more performance, you could try to build `dmjit` with PGO (Rust book [link](https://doc.rust-lang.org/rustc/profile-guided-optimization.html)). A similar project like [CPython](https://github.com/python/cpython) already uses PGO, so it definitely should be applicable to `dmjit` as well.