* winch(fuzz): Initial support for differential fuzzing
This commit introduces initial support for differential fuzzing for Winch. In
order to fuzz winch, this change introduces the `winch` cargo feature. When the
`winch` cargo feature is enabled the differential fuzz target uses `wasmi` as
the differential engine and `wasm-smith` and `single-inst` as the module sources.
The intention behind this change is to have a *local* approach for fuzzing and
verifying programs generated by Winch and to have an initial implementation that
will allow us to eventually enable this change by default. Currently it's not
worth it to enable this change by default given all the filtering that needs to
happen to ensure that the generated modules are supported by Winch.
It's worth noting that the Wasm filtering code will be temporary, until Winch
reaches feature parity in terms of Wasm operators.
* Check build targets with the `winch` feature flag
* Rename fuzz target feature to `fuzz-winch`
a1732b2906