Revert let_chains stabilization

[Noratrieb]

This is the revert against master, the beta revert was already done in #100538.

Bumps the stage0 compiler which already has it reverted.

[rust-highfive]

r? @Mark-Simulacrum

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[rustbot]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

Examples of T-libs-api changes:

• Stabilizing library features
• Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
• Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
• Changing public documentation in ways that create new stability guarantees
• Changing observable runtime behavior of library APIs

rustc_error_messages was changed

cc @davidtwco, @compiler-errors, @JohnTitor, @estebank

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[hkmatsumoto]

Removing A-translation label which looks unrelated.

[Mark-Simulacrum]

@bors r+ rollup=iffy

[bors]

📌 Commit aa0b40ef6c70f29a2c98a9faa2b6b7cd706ab120 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

☔ The latest upstream changes (presumably #100868) made this pull request unmergeable. Please resolve the merge conflicts.

[Noratrieb]

I'm a little busy this week, I should get to it next week.

[Noratrieb]

@Mark-Simulacrum done, I also migrated the one "new" diagnostic to session diagnostics.

Also, I think this should probably get p=1 since this is pretty bitrotty as it seems

[compiler-errors]

@bors r=Mark-Simulacrum rollup=never p=1

[bors]

📌 Commit 01acfef has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

⌛ Testing commit 01acfef with merge a0d0709...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing a0d0709 to master...

[rust-timer]

Finished benchmarking commit (a0d0709): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.3%, -1.2%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	9.2%	[9.2%, 9.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²