Allow -Z treat-err-as-bug=0

[ShE3py]

Makes -Z treat-err-as-bug=0 behave as if the option wasn't present instead of asking the value to be ⩾ 1. This enables a quick on/off of the option, as you only need to change one character instead of removing the whole -Z.

Also update some text, e.g.

$ rustc -Z help | grep treat-err-as-bug
    -Z                      treat-err-as-bug=val -- treat error number `val` that occurs as bug

where the value could be interpreted as an error code instead of an ordinal.

[rustbot]

r? @petrochenkov

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[ShE3py]

I tried another wording for the option's description, but it's kinda verbose now.

@rustbot review

[petrochenkov]

r=me after squashing commits.
@rustbot author

[petrochenkov]

@bors r+

[bors]

📌 Commit 3dd0419 has been approved by petrochenkov

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3dd0419 with merge 0190394...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 0190394 to master...

[rust-timer]

Finished benchmarking commit (0190394): 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)	3.5%	[3.0%, 3.7%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
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)	-	-	0
Regressions ❌ (secondary)	2.7%	[2.1%, 3.1%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 634.55s -> 633.528s (-0.16%)
Artifact size: 317.65 MiB -> 317.74 MiB (0.03%)