move to the new unified wasmtime repository for cranelift git submodule

[froydnj]

As part of the ongoing work to make lucetc work for Windows, cranelift has had some APIs added to enable using cranelift-module for some of lucetc's work, rather than cranelift-faerie. To update lucetc to take advantage of those APIs, it's necessary to use the new unified wasmtime repo...which also involves dealing with the API changes between the cranelift crate versions currently in use and the upstream versions.

I'm happy to do this work (although if somebody's already in-process, I'll gladly step aside!), but are there any external constraints I need to know about before getting too far into the weeds?

[pchickey]

None of us at Fastly have gotten to updating that repo lately, but there are no other external constraints that we are aware of. Go for it!

[pchickey]

Oh, one constraint I am aware of: we're not ready to use the version of wasi-common in the wasmtime tree quite yet, so please keep that one at version 0.7. I don't believe that will conflict with anything else in the wasmtime tree.

[pchickey]

Oh, one other thing we just thought of: using cranelift as a submodule versus a crates.io dependency is a historical artifact, from back when we were making lots of cranelift changes. Its not actually very useful anymore to have it as a submodule. So, rather than replace it with a wasmtime submodule, maybe now is a good time to just switch to depending only on the published crates. If we end up needing to patch something down the road, we'll use cargo's patch features for it.