transmute size check: properly account for alignment

[RalfJung]

Fixes another place where ZST alignment was ignored when checking whether something is a newtype. I wonder how many more of these there are...

Fixes #101084

[rustbot]

r? @pnkfelix

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[RalfJung]

r? compiler

[Nadrieril]

Looks reasonable but I'm not competent in this

r? compiler

[oli-obk]

r? @oli-obk

While the error message doesn't state the reason, that is preexisting with all the other cases and needs an approach for all sites

[bors]

📌 Commit 9f0c7f0 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 9f0c7f0 with merge bda221a...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing bda221a to master...

[rust-timer]

Finished benchmarking commit (bda221a): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.2%	[2.8%, 5.6%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 3.4%, secondary 3.1%)

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)	3.4%	[3.4%, 3.4%]	1
Regressions ❌ (secondary)	3.1%	[1.4%, 5.0%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.4%	[3.4%, 3.4%]	1

Cycles

Results (primary 2.9%, secondary -2.3%)

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)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-7.7%	[-7.7%, -7.7%]	1
All ❌✅ (primary)	2.9%	[2.9%, 2.9%]	1

Binary size

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

Bootstrap: 694.699s -> 693.956s (-0.11%)
Artifact size: 326.68 MiB -> 324.65 MiB (-0.62%)