Update `catch_unwind` doc comments for `c_unwind` Updates `catch_unwind` doc comments to indicate that catching a foreign exception _will no longer_ be UB. Instead, there are two possible behaviors, though it is not specified which one an implementation will choose. Nominated for t-lang to confirm that they are okay with making such a promise based on t-opsem FCP, or whether they would like to be included in the FCP. Related: https://github.com/rust-lang/rust/issues/74990, https://github.com/rust-lang/rust/issues/115285, https://github.com/rust-lang/reference/pull/1226