doc: linker-plugin-based LTO: update list of good combinations

[zamazan4ik]

This PR is similar to #146827 . I just ran the Python script as was recommended in this comment. Also updated the LOWER_BOUND in the script to skip a bit redundant work in the Python script.

@nnethercote pinging you as a reviewer here since the last time you did it too ;)

[rustbot]

r? @JohnTitor

rustbot has assigned @JohnTitor.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @ehuss, compiler
• @ehuss, compiler expanded to 70 candidates
• Random selection from 12 candidates

[Copilot]

Pull request overview

Updates the rustc documentation for linker-plugin-based LTO by refreshing the “known good” Rust↔Clang/LLVM version combinations and slightly adjusting the helper script used to regenerate that table.

Changes:

• Bump the Python script’s LOWER_BOUND to reduce redundant work when regenerating the compatibility table.
• Update the compatibility table to extend the LLVM 21 range through Rust 1.94.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

View changes since this review

[Copilot]

The update script only generates rows starting at LOWER_BOUND. With LOWER_BOUND = 91 it’s easy for someone to re-run the script and accidentally replace the whole table with only 1.91+ entries. Consider adding a short note near LOWER_BOUND explaining that earlier rows are intentionally kept static / should be preserved when updating, or set LOWER_BOUND to the earliest version covered by the table when doing a full regeneration.

Suggested change

	# NOTE: The table in this document may contain entries for Rust versions
	# earlier than LOWER_BOUND. Those earlier rows are intentionally kept
	# static and are not regenerated by this script. When updating the table,
	# preserve any rows for versions < LOWER_BOUND, or, if you want to fully
	# regenerate the table, first set LOWER_BOUND to the earliest minor version
	# you wish to cover.

[zamazan4ik]

Related issue - #154285 (but this PR does not fix the issue)