Cranelift: Runtests should automatically run with and without optimizations

> A bit of an aside, but it also makes me think that we should make the runtest runner automatically run tests twice, once with optimizations and once without them. Because we want that for every single runtest that exercises any mid-end rewrite rule, and it definitely doesn't hurt for runtests that are just stressing lowering or something.

_Originally posted by @fitzgen in https://github.com/bytecodealliance/wasmtime/pull/6879#pullrequestreview-1589793608_