[Issue 22439] New: OpenBSD: Sync mman.d

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22439

          Issue ID: 22439
           Summary: OpenBSD: Sync mman.d
           Product: D
           Version: D2
          Hardware: All
                OS: Other
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody at puremagic.com
          Reporter: bcallah at openbsd.org

Sync DRuntime's OpenBSD mman.d with OpenBSD's mman.d
Adds MAP_CONCEAL
Syncs MAP_FLAGMASK
Removes mincore (doesn't exist on OpenBSD)

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