rustc_log: provide a way to init logging based on the values, not names, of the env vars

[RalfJung]

Miri wants to affect how rustc does logging. So far this required setting environment variables before calling rustc_driver::init_rustc_env_logger. However, set_var is a function one should really avoid calling, so this adds the necessary APIs to rustc such that Miri can just pass it the values of all the log-relevant environment variables, rather than having to change the global environment.

[rustbot]

r? @TaKO8Ki

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[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[TaKO8Ki]

@bors r+

[bors]

📌 Commit 86e5d36 has been approved by TaKO8Ki

It is now in the queue for this repository.

[bors]

⌛ Testing commit 86e5d36 with merge ee85f7f...

[bors]

☀️ Test successful - checks-actions
Approved by: TaKO8Ki
Pushing ee85f7f to master...

[rust-timer]

Finished benchmarking commit (ee85f7f): 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)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.4%	[-3.6%, -3.3%]	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: 674.6s -> 675.537s (0.14%)
Artifact size: 311.10 MiB -> 311.09 MiB (-0.00%)