This adds a `--always-lightbeam` option as well as an `--always-cranelift` option, to allow the compilation strategy to be selected via the command-line. This also enables regular testing for Lightbeam.
This is the wasmtime-jit crate, which contains JIT-based execution
for wasm, using the wasm ABI defined by wasmtime-environ and the
runtime support provided by wasmtime-runtime.