Fix Issue 22439 - OpenBSD: Sync mman.d

[ibara]

No description provided.

[dlang-bot]

Thanks for your pull request and interest in making D better, @ibara! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	22439	enhancement	OpenBSD: Sync mman.d

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + druntime#3596"