Restore compatibility with upstream disas tests

[frank-emrich]

It recently became necessary to regenerate the expected output of most (all?) of the files in tests/disas. Concretely, we were generating slightly different CLIF than upstream even on modules not involving any WasmFX instructions.

This PR rectifies this situation, making sure that we generate identical CLIF again. This required two changes:

Global CLIF variable for runtime limits pointer

Since #99, we called the function wasmtime_cranelift::func_environ::FuncEnvironment::declare_vmruntime_limits_ptr unconditionally for every compiled function, meaning that every function prelude now contained a definition of the corresponding global variable.

This PR changes this behavior: I restored the original logic for when to call declare_vmruntime_limits_ptr. Instead of using the global variable vmruntime_limits to access the VMRuntimeLimits, we now load this pointer ourselves once per resume instruction. Since the load instruction is marked as readonly, it should be coalesced into a single load, even if multiple resumes appear in the same function.

I've benchmarked this, using a micro-benchmark with 2 resume instructions in the same function, and as expected there is no observable difference in performance.

Order of libcall declarations

In builtin.rs, we put the declarations of our own libcalls into the middle of the list of all libcalls in the foreach_builtin_function macro. This shifted the indices of some existing libcalls, which caused the CLIF to differ when using these. I've moved all the tc_ libcalls to the end of the list, thus leaving the indices of existing libcalls unchanged.

As a result, I've replaced all files in tests/disas with the versions from upstream (bytecodealliance/wasmtime@afaf1c7, the most recent upstream commit that we've merged)

[dhil]

LGTM.