Revert "Mark atomics as unsupported on thumbv6m"

[Amanieu]

This is a breaking change for the thumbv6m target. See #99668 for discussion on how we can proceed forward from here.

This reverts commit 7514610.

cc @nikic

[rust-highfive]

r? @oli-obk

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[rust-highfive]

⚠️ Warning ⚠️

• These commits modify compiler targets. (See the Target Tier Policy.)

[nikic]

@bors r+

[bors]

📌 Commit d931a58 has been approved by nikic

It is now in the queue for this repository.

[Amanieu]

Let's ensure this makes it into the next nightly.

@bors p=1

[bors]

⌛ Testing commit d931a58 with merge c32dcbb...

[bors]

☀️ Test successful - checks-actions
Approved by: nikic
Pushing c32dcbb to master...

[rust-timer]

Finished benchmarking commit (c32dcbb): comparison url.

Instruction count

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 😿 relevant regression found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	0.3%	0.3%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	N/A	N/A	0

Max RSS (memory usage)

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: 🎉 relevant improvement found

	mean1	max	count2
Regressions 😿 (primary)	3.2%	3.2%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-3.9%	-3.9%	1
All 😿🎉 (primary)	3.2%	3.2%	1

Cycles

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: no relevant changes found

	mean1	max	count2
Regressions 😿 (primary)	2.5%	2.5%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	2.5%	2.5%	1

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

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³