Use catch_unwind in the FFI

[thomcc]

It's undefined behavior for us to unwind into C, which is extremely bad news.

[ncalexan]

A quick read shows that catch_panic is unstable, so we can't do this quite yet. In the interim, do you know what the best approach is? And even when catch_panic is available, is the content of this ticket that we need to wrap every FFI entry point that might panic with a closure?

[thomcc]

Sorry, the stable name is catch_unwind. https://doc.rust-lang.org/std/panic/fn.catch_unwind.html

is the content of this ticket that we need to wrap every FFI entry point that might panic with a closure?

Yes. Which in practice probably means almost all of them, if not all.