wasm2c: add hook to allow a custom trap handler

[shravanrn]

In production use cases, unwinding the stack before reporting an error throws away valuable information such as the stack trace. This hook allows the host to implement an alternate error recovery/reporting mechanism

[sbc100]

Can we have a test for this, and also add it to the README?

[shravanrn]

@sbc100 Hmm... I only see the wasm spec tests, and I think this test looks a little different as this testing the embedder API. Are there any existing tests for the embedder API, which I can use as an example?

[sbc100]

Good question. Maybe we don't have good way to test this right now. We have at least one other change outstanding that is also blocked on a good testing strategy: #2009.

I think change is pretty small and probably doesn't need to be blocked on coming up with a new way to test wasm2c features, but we should probably be thinking about this. @keithw did you have any ideas for wasm2c testing outside of the existing run-spec-wasm2c tests?

[keithw]

@keithw did you have any ideas for wasm2c testing outside of the existing run-spec-wasm2c tests?

I think it's pretty doable (e.g. we could make an option to run-spec-wasm2c.py to have it accept an arbitrary main.c given on stdin, or something like that).