Implement real jump tables

[pepyakin]

There is this panic

https://github.com/CraneStation/wasmtime/blob/c5f0cd7d5e350afe4dd2d18e8efc009ad7f1eae3/lib/environ/src/compilation.rs#L66-L73

what is this about? I've tried to use a simple br_table with a few arms and it seems to work fine.

[sunfishcode]

br_table is currently implemented by lowering it into a bunch of conditional branches. #453 is working on implementing it with an actual jump table.

[pepyakin]

Cool, thanks for the info! So then we need to implement relocating jump tables after they land in cranelift: bytecodealliance/cranelift#453.

I will update this issue and #14

[pepyakin]

I believe this is implemented.