Find a way to write tests for asserting certain LLVM output

[yorickpeterse]

As we start adding LLVM attributes, enabling optimizations and so on, it would be nice if we could include a set of tests that assert that given Inko source code A we get LLVM output B.

While we have the ability to dump the LLVM IR, the IR itself is incredibly noisy and prone to random unrelated changes such that I suspect we'll run into frequent random test failures. We need something more stable, such that the tests only fail if in fact the output is different. I'm not yet sure what that something would be.