bae0257fc3
We weren't previously keeping track of quite the right information for whether an `if .. else .. end`'s following block was reachable or not. It should be reachable if the head is reachable and either the consequent or alternative end reachable (and therefore fall through to the following block) or do an early `br_if` to it. This commit rejiggers `ControlStackFrame::If` to keep track of reachability at the end of the consequent (we don't need to keep track of it at the end of the alternative, since that is simply `state.reachable`) and adds Wasm tests for every reachability situation we can encounter with `if .. else .. end`. Fixes #1132