Cranelift: test/fuzz our ABI/calling convention code with ABI cafe

[fitzgen]

Very neat project: https://github.com/Gankra/abi-cafe

[afonso360]

We already do this indirectly via cg_clif! (It would still be nice to have it locally in CI)

[bjorn3]

Using abi-cafe without cg_clif intermediate would require writing a new backend for abi-cafe that uses cranelift to compile object files. This shouldn't be too hard as there are already C and Rust backends, but it will require maintaining a fork of abi-cafe.