* Remove the `Flags` type from `Config` API
This commit removes the final foreign type from the `Config` API in the
`wasmtime` crate. The cranelift `Flags` type is now expanded into
various options on the `Config` structure itself, all prefixed with
`cranelift_` since they're only relevant to the Cranelift backend. The
various changes here were:
* The `avoid_div_traps` feature is enabled by default since it seemed
that was done anywhere anyway.
* Enabling the wasm SIMD feature enables the requisite features in
Cranelift as well.
* A method for enabling the debug verifier has been added.
* A method for configuring the Cranelift optimization level, as well as
a corresponding enumeration, has been added.
* Assert that `Config` is both `Send` and `Sync`
41528c82bc