Tracking issue for release notes of #151994: switch to v0 mangling by default on stable

[rustbot]

This issue tracks the release notes text for #151994.

cc @davidtwco, @wesleywiser -- original issue/PR authors and assignees for drafting text

See the forge.rust-lang.org chapter about release notes for an overview of how the release team makes use of these tracking issues.

Release notes text

This section should be edited to specify the correct category(s) for the change, with succinct description(s) of what changed. Some things worth considering:

• Does this need an additional compat notes section?
• Was this a libs stabilization that should have additional headers to list new APIs under Stabilized APIs and Const Stabilized APIs?

# Compatibility Notes
- [Rust will use the v0 symbol mangling scheme by default.](https://github.com/rust-lang/rust/pull/151994) This may cause some tools (such as debuggers or profilers, especially with old versions) to fail to demangle symbols emitted by Rust. It may also cause the formatting of text in backtraces to change.

Tip

Use the previous releases for inspiration on how to write the release notes text and which categories to pick.

Release blog section

If this change is notable enough for inclusion in the blog post then this section should be edited to contain a draft for the blog post. Otherwise leave it empty.

rustc now defaults to the "v0" symbol mangling scheme, instead of our previous default which was based on the Itanium ABI naming mangling scheme used by C++. Our v0 mangling scheme has been [the default on nightly releases of Rust since November 2025](https://blog.rust-lang.org/2025/11/20/switching-to-v0-mangling-on-nightly/). This should improve the experience of using Rust with debuggers and profilers that work with compiled Rust binaries.

Note

If a blog post section is required the release-blog-post label should be added (@rustbot label +release-blog-post) to this issue as otherwise it may be missed by the release team.

[theemathas]

This should also mention that backtraces will change slightly. See #157432.