[Issue 18924] Use addition rather than XOR for order-independent hash combination

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18924

--- Comment #1 from Nathan S. <n8sh.secondary at hotmail.com> ---
Pull request: https://github.com/dlang/druntime/pull/2199

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