[DO NOT MERGE] Test njn's hashbrown changes on CI

[lqd]

This is a CI hack on top of hacks, to try and get njn's build using a hashbrown fork profiled on CI.

r? @ghost

[lqd]

@bors try

[bors]

⌛ Trying commit 18bbde0 with merge 7f2f2f7e1a8b9a1c3e3329facd5fc84e11f5da4d...

[bors]

☀️ Try build successful - checks-actions
Build commit: 7f2f2f7e1a8b9a1c3e3329facd5fc84e11f5da4d (7f2f2f7e1a8b9a1c3e3329facd5fc84e11f5da4d)

[lqd]

Might as well trigger the perf run now, since the collector's queue is empty

@rust-timer build 7f2f2f7e1a8b9a1c3e3329facd5fc84e11f5da4d

[rust-timer]

Queued 7f2f2f7e1a8b9a1c3e3329facd5fc84e11f5da4d with parent b03c504, future comparison URL.

[rust-timer]

Finished benchmarking commit (7f2f2f7e1a8b9a1c3e3329facd5fc84e11f5da4d): comparison url.

Summary: This change led to very large relevant mixed results 🤷 in compiler performance.

• Very large improvement in instruction counts (up to -9.2% on incr-patched: println builds of webrender)
• Large regression in instruction counts (up to 2.7% on full builds of wg-grammar)

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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 led to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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