fail does not typecheck at the WebAssembly level

[ospencer]

At the WebAssembly level, Grain "any" types are i32s but this block needs to return an i64 like the others. We got around this before by this being a call_indirect—we just lied about what type fail returned. At runtime, instead of raising Failure, this is a call_indirect typechecking error.

Essentially, we need a compiler primitive for fail which can print the error and then generate unreachable. (But we can't do that until the enum refactor is done because Failure would need to be baked into the compiler.)

Originally posted by @ospencer in #1175 (comment)