* Upgrade all crates to the Rust 2021 edition
I've personally started using the new format strings for things like
`panic!("some message {foo}")` or similar and have been upgrading crates
on a case-by-case basis, but I think it probably makes more sense to go
ahead and blanket upgrade everything so 2021 features are always
available.
* Fix compile of the C API
* Fix a warning
* Fix another warning
This crate provides a straightforward way to create a
Cranelift IR function and fill it with
instructions translated from another language. It contains an SSA construction
module that provides convenient methods for translating non-SSA variables into
SSA Cranelift IR values via use_var and def_var calls.