Tracking Issue for `-Ctarget-feature=+backchain`

This is a tracking issue for the -Ctarget-feature=+backchain feature on s390x.

About tracking issues

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 about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Implement. backchain is already fully implemented. However there is cross influence with other flags and features. (see #152432 and #151154)
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

None

Implementation history

• #152432
• #151154
• #127506

Start with the linked rustc-dev-guide stabilization and documentation instructions, then review implementation history in #152432, #151154, and #127506. The feature is implemented; done means completing the documentation adjustment and preparing the stabilization PR for the s390x -Ctarget-feature=+backchain feature.