Tracking issue for MCP 1019: Emit `note` when calling `rustc` without specifying an edition

This is a tracking issue for MCP "Emit note when calling rustc without specifying an edition" (rust-lang/compiler-team#1019).

[!NOTE]
Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.

A tracking issue is however not meant for large scale discussion, questions, or bug reports.
Instead, open a dedicated issue for the specific matter, link to this tracking issue and ping the MCP author.
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Discussion comments will get marked as off-topic or deleted.
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Steps

• Implement the MCP
• Adjust the documentation
  • In the Rust Compiler Development Guide if applicable (e.g., for refactorings)
  • In the Rust Forge if applicable (e.g., for policy changes)
  • In the rustc book if applicable (e.g., for target tier or CLI changes)
  • In the Unstable Book if applicable (e.g., for unstable CLI changes)

Unresolved questions

None so far.

Implementation history

Empty so far.

@estebank, consider @rustbot claim'ing the work.

Start by reading MCP "Emit note when calling rustc without specifying an edition" and the rustc CLI documentation. Identify the implementation and documentation work required, then verify the MCP is implemented and the applicable Compiler Development Guide, Rust Forge, rustc book, or Unstable Book entries are updated.