[stable] Allow detached threads to be joined on Windows too

[kinke]

PR #3418 allowed them on Posix; extend it to Windows too. The added test/thread/src/join_detach.d test now passes on Windows (tested by LDC).

[dlang-bot]

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Testing this PR locally

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dub run digger -- build "stable + druntime#3429"

[Geod24]

Sweet, thanks!