[Issue 18923] Semaphore internal handle should be `protected` instead of `private`

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18923

github-bugzilla at puremagic.com changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

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