Rust's standard library now has a way to read the OS errno value, so use that instead of depending on the errno crate in wasmtime-runtime.
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.