refactor(cranelift-codegen): remove OnceLock

[JonasKruckenberg]

This removes the dependency on std::sync::OnceLock by lifting the state out of a static and into the Callee struct.

This PR also removes the call_conv parameter since it was not used by any of the trait implementations.

[alexcrichton]

ping @elliottt (or other cranelift folks on this), I don't know enough about MachineEnv myself to know if the lift here is reasonable to apply

[cfallin]

This could possibly result in a performance degradation in the compiler: it removes the caching of the MachineEnv, which contains lists of registers (heap-allocated Vecs), and recreates it for each function that is compiled. Especially for small functions this could be a measurable/non-negligible portion of the total work.

@JonasKruckenberg, could you say more about the motivation here? And have you measured the performance impact?

[JonasKruckenberg]

Yeah thats a concern I had too.
The motivation is to support #8341 and since OnceLock is the only thing in cranelift that cant be ported to no_std+alloc or gated behind flags the idea was to replace it by something else.
Adding another dependency on something like spin for no_std targets doesn't seem appropriate either.

I'll do some benchmarking next week and report back 👍

[cfallin]

Ah, one other option could be to put it in the MachBackend instead -- if it's the case that it no longer depends on the call_conv. If it does on some backends (x64 might differentiate with fastcall?), we could statically construct the various options. That way, it's constructed once per compiler session, but without the lazy init.