disable download-rustc if LLVM submodule has changes in CI

[onur-ozkan]

We can't use CI rustc while using in-tree LLVM (which happens in LLVM submodule update PRs) and this PR handles that by ignoring CI-rustc in CI and failing in non-CI environments.

[rustbot]

r? @Kobzol

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[rustbot]

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

[onur-ozkan]

Tested and it's fixed #131448 (comment) in #131455.

[Kobzol]

Looks reasonable. As usually, I would like to move this logic outside of Config parsing, but that can happen later (once I can finally get to is, sigh..).

@bors r+

[bors]

📌 Commit b198a46 has been approved by Kobzol

It is now in the queue for this repository.

[bors]

⌛ Testing commit b198a46 with merge de19f2b...

[bors]

☀️ Test successful - checks-actions
Approved by: Kobzol
Pushing de19f2b to master...

[rust-timer]

Finished benchmarking commit (de19f2b): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (secondary 2.2%)

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.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

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

Binary size

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

Bootstrap: 774.605s -> 775.399s (0.10%)
Artifact size: 329.57 MiB -> 329.69 MiB (0.03%)