Previously we initialized trap handling (signals/etc) once-per-instance but that's a bit too granular since we only need to do this as one-time per-program initialization. This moves the initialization to `Store` instead which means that we'll call this at least once per thread, which some platforms may need (none currently do, they all only need per-program initialization, but Fuchsia will need per-thread initialization).
This is the wasmtime-runtime crate, which contains wasm runtime library
support, supporting the wasm ABI used by wasmtime-environ,
wasmtime-jit, and wasmtime-obj.
This crate does not make a host vs. target distinction; it is meant to be compiled for the target.
Most users will want to use the main wasmtime crate instead of using this
crate directly.