Tracking issue for release notes of #128321: Update catch_unwind doc comments for c_unwind

[rustbot]

This issue tracks the release notes text for #128321.

• Proposed text is drafted by PR author (or team) making the noteworthy change.
• Issue is nominated for release team review of clarity for wider audience.
• Release team includes text in release notes/blog posts.

Release notes text:

The responsible team for the underlying change should edit this section to replace the
automatically generated link with a succinct description of what changed, drawing upon text
proposed by the author (either in discussion or through direct editing). If the change is notable
enough for inclusion in the blog post, add content to the blog section below.

# Pick a category...
- [Update `catch_unwind` doc comments for `c_unwind`](https://github.com/rust-lang/rust/pull/128321)

Note: The section title will be de-duplicated by the release team with other release notes issues.
Please use a standard title from previous releases.
More than one section can be included if needed.

Release blog section (if any, leave blank if no section is expected):

cc @BatmanAoD, @Mark-Simulacrum -- origin issue/PR authors and assignees for starting to draft text

[BatmanAoD]

I suppose the thing to mention in the release notes is that using catch_unwind is no longer considered UB?

(Since the implementation isn't changing, do we consider this guarantee to be retroactively applicable to 1.81 and/or even further back?)