411 simple integration test using old simple rust programs

[jberthold]

This PR adds a set of simple rust programs (from prior art) for a simple parser test:

• salvages old test programs from run-rs in the textual-mir branch
• sets up smir_pretty as a submodule for integration tests
• adds make targets to manage the submodule build (including a bootstrap of rustc, which should be set up as a recursive submodule in the future)
• adds a make target for a simple integration test: convert each run-rs program to Stable-MIR and parse the result.

Remarks:

• The tests are currently only proving that the parser succeeds. We can add better checks later when the format is stable enough to not cause noise in golden tests.
• In order to run smir_pretty, information about the rust target architecture is needed. To circumvent this, the related script (within smir_pretty repo) is patched (but only the copy in the docker file system). This is a workaround and could be addressed properly by
  • crafting a github action to set up K and removing the dockerised K,
  • or preparing smir_pretty to run within nix and using a nix shell.
  • or (not recommended) placing the custom rust build and smir_pretty within the docker image or container.

[dkcumming]

I will let you choose when to merge @jberthold in case there was more commits to add