Copy stage0 rustc binaries to stage0-sysroot

[Kobzol]

This is basically a revival of #101711 and #107956, with an added check that the full sysroot will only be created if the original rustc comes from stage0/bin.

What is/should be tested:

• rustup toolchain link stage0 (new libstd is used correctly)
• python3 x.py fmt dist --stage 0
• Custom rustc/cargo in config.toml (in this case this logic is ignored)
• Perfbot (try perf run has succeeded)
• Real use case (CI: add workflow for checking binary size backtrace-rs#542)

(Hopefully) fixes: #101691

This is not the "end all, be all" solution to this problem, but as long as it resolves the basic use-case, and doesn't break perfbot, I say ship it. This code will probably be nuked anyway Soon™ because of the stage redesign.

[rustbot]

r? @Mark-Simulacrum

(rustbot has picked a reviewer for you, use r? to override)

[Kobzol]

@bors try @rust-timer queue

[bors]

⌛ Trying commit bb8c497 with merge 4326a1077ebab6adbc37556763a8fd302d86f154...

[bors]

☀️ Try build successful - checks-actions
Build commit: 4326a1077ebab6adbc37556763a8fd302d86f154 (4326a1077ebab6adbc37556763a8fd302d86f154)

[rust-timer]

Finished benchmarking commit (4326a1077ebab6adbc37556763a8fd302d86f154): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

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.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-	-	0

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.

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Binary size

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

Bootstrap: 653.846s -> 654.334s (0.07%)

[Kobzol]

Ok, perf seems to work, hopefully the conservative approach taken here will not break it.

@rustbot ready

[Mark-Simulacrum]

@bors r+ rollup=iffy

[bors]

📌 Commit bb8c497 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

⌛ Testing commit bb8c497 with merge 1065d87...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 1065d87 to master...

[rust-timer]

Finished benchmarking commit (1065d87): 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

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-2.8%, -2.8%]	2
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: 657.324s -> 659.399s (0.32%)