[Issue 19904] move semantics fail through the `emplace` pipeline

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19904

--- Comment #8 from kinke <kinke at gmx.net> ---
I completely forgot about this; it should be fixed now. The struct case was
already handled, the class case was recently fixed with
https://github.com/dlang/druntime/pull/3352.

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