Since this feature is now merged into the upstream wasm spec it
makes sense to enable it by default, at least for the default CPU.
The mvp CPU can still be used to avoid this feature.
See: https://github.com/WebAssembly/spec/pull/1143
This is just to test the water and the plan is to enable all features
that have been merged, assuming this change is accepted.
It seems strange to change the default here. x86 initializes all its corresponding features to false then selectively enables them in initFeatureMap. I think we should stick with that pattern if possible.