[Issue 18921] make core.internal.hash cater to memberwise hash chaining

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18921

--- Comment #1 from Nathan S. <n8sh.secondary at hotmail.com> ---
Pull request: https://github.com/dlang/druntime/pull/2198

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