Finish up Miri integration

[Aaron1011]

This PR gets all of the tests passing under Miri, and runs them on CI.

[Aaron1011]

@alexcrichton: How do you want to handle the case where Miri is not available for a given channel?

[alexcrichton]

Thanks for this! Could a new CI builder be added with a pinned nightly version to handle drift in miri?

[Aaron1011]

@RalfJung What's the preferred way to handle this kind of thing? Is there a way to get Rustup to automatically install the most recent nightly that has Miri available?

[RalfJung]

Is there a way to get Rustup to automatically install the most recent nightly that has Miri available?

Yes, it is described in our README:

MIRI_NIGHTLY=nightly-$(curl -s https://rust-lang.github.io/rustup-components-history/x86_64-unknown-linux-gnu/miri)
echo "Installing latest nightly with Miri: $MIRI_NIGHTLY"
rustup set profile minimal
rustup default "$MIRI_NIGHTLY"
rustup component add miri

[Aaron1011]

@alexcrichton: This should be ready to merge

[alexcrichton]

👍