Fix DDOC comments in core/stdc/errno.d

[MoonlightSentinel]

No description provided.

[dlang-bot]

Thanks for your pull request and interest in making D better, @MoonlightSentinel! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
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• My PR is fully covered with tests (you can see the coverage diff by visiting the details link of the codecov check)
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Testing this PR locally

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dub run digger -- build "master + druntime#3088"

[schveiguy]

I can't tell from the diff whether the comments all were preserved, but I'm not going to worry about it.

[MoonlightSentinel]

I used regex search+replace so there should be no issues here

[schveiguy]

I'd like to merge this, but the circleci build seems to have a spurious failure.

[Geod24]

@schveiguy : Retriggered the CI for you. You should be able to do it from CircleCI interface though.

[schveiguy]

I looked, but even though it said I was logged in, it didn't give me options to retry.

Edit: just went in again, I must have been logged in some other way, because I logged out and back in and now I see the rerun button.