Tracking Issue for `naked_functions_target_rustic_abi`

[folkertdev]

The feature gate for the issue is #![feature(naked_functions_target_rustic_abi)].

Because the details of the rust abi are unstable, and a naked function must match its stated ABI, this feature gate keeps naked functions with a rustic abi ("Rust", "rust-cold", "rust-call" and "rust-intrinsic") unstable.

Splitting out this feature was decided on in https://hackmd.io/20YsMoNgRjyxhBm_aVEwQg#Stabilize-naked_functions-rust134213.

About tracking issues

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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 about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
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Steps

• Implement the RFC (cc @rust-lang/XXX -- can anyone write up mentoring
  instructions?)
• Adjust documentation (see instructions on rustc-dev-guide)
• Formatting for new syntax has been added to the Style Guide (nightly-style-procedure)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

XXX --- list all the "unresolved questions" found in the RFC to ensure they are
not forgotten

Implementation history

@rustbot label +A-naked +F-naked_functions