cranelift: Expand `clif-util bugpoint` to minimize runnable test cases

👋 Hey,

#### Feature

bugpoint is a really interesting tool if some clif code is failing to compile. Some of outputs reported by the clif differential fuzzer don't fail to compile, but predictably crash during execution. We could expand bugpoint to iterate while the run keeps crashing.

#### Benefit

This would help a lot minimizing the test cases dumped by the clif fuzzer. The fuzzing engine isn't very good at minimizing those cases.

#### Implementation

I'm not too familiar with bugpoint, but I guess we can add a mode that besides compiling does something similar to what `clif-util test` does. We would have to catch panics and exceptions thrown during execution and probably ensure that they don't change while iterating.

#### Alternatives

Minimizing by hand is kinda painful but we can keep doing it.