Jitted runs do not terminate cleanly

[eggyal]

Because rustc_codegen_cranelift::driver::jit::run_jit never returns, rustc never runs finalisation actions for jitted runs; e.g. the incremental compilation cache is not committed to disk (in particular, rustc_interface::interface::Compiler::enter never progresses from invoking the passed f closure to the subsequent save_dep_graph call).

[bjorn3]

This is fixed on my wip hotswap branch. I don't think I will have time to work much on it the next month or so due to exams unfortunately.