Fix table issues in platform support documentation (closes #115047)

[Kriskras99]

mdBook needs an empty line before and after the table block.
In addition, in the tier-3 list three targets forgot about the host column and therefore showed the notes in the host column.

Closes #115047

[rustbot]

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[ehuss]

Thanks!

@bors r+ rollup

[bors]

📌 Commit dfbac25 has been approved by ehuss

It is now in the queue for this repository.

[matthiaskrgr]

@bors r-
looks like this failed in #115068 (comment)

[Kriskras99]

@matthiaskrgr:

@bors r- looks like this failed in #115068 (comment)

I think the pull request that failed was #115011, this pull request only changes some markdown files in the rustc book.

[matthiaskrgr]

Ooh sorry, yes makes sense :)
@bors r=ehuss

[bors]

📌 Commit dfbac25 has been approved by ehuss

It is now in the queue for this repository.

[bors]

⌛ Testing commit dfbac25 with merge 32aa405...

[bors]

☀️ Test successful - checks-actions
Approved by: ehuss
Pushing 32aa405 to master...

[rust-timer]

Finished benchmarking commit (32aa405): 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)	1.3%	[1.3%, 1.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.4%, -1.4%]	1
All ❌✅ (primary)	1.3%	[1.3%, 1.3%]	1

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: 634.501s -> 634.782s (0.04%)
Artifact size: 347.06 MiB -> 347.03 MiB (-0.01%)