Enable miri in CI and run miri tests in CI

[kkysen]

In #686, I tried to add a miri test, which would be run in CI like the others, but I get a permission denied error from miri running in CI when or right after it installs xargo. Furthermore, it'd probably be a good idea to install xargo beforehand so it doesn't have to be re-installed every time. The miri test is #[ignore]d for now, but ideally, it'd be enabled so we don't accidentally re-introduce UB and flakiness into the analysis/test tests.

[bytewife]

Hi! Where is the miri test located?

[kkysen]

The miri test is here:

c2rust/pdg/src/main.rs

Lines 387 to 397 in 5ce9db6

	#[test]
	#[ignore]
	fn analysis_tests_misc_miri() -> eyre::Result<()> {
	init();
	let mut cmd = Command::new("cargo");
	cmd.current_dir(repo_dir()?.join("analysis/tests/misc"))
	.args(&["miri", "run", "--features", "miri"])
	.env("MIRIFLAGS", "");
	let status = cmd.status()?;
	ensure!(status.success(), eyre!("{cmd:?} failed: {status}"));
	Ok(())

You can run it with cargo test -p c2rust-pdg -- --ignored tests::analysis_tests_misc_miri.

[kkysen]

miri seems to longer use xargo as of rust-lang/miri#2564, so if we upgrade our nightly version past around nightly-2022-09-24, we should sidestep the xargo installation issue. We'll see if there's still an issue after that.