[Issue 18899] destroy is inefficient for small structs

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18899

--- Comment #9 from Manu <turkeyman at gmail.com> ---
True.
Anyway, I'm just playing devils advocate. I agree, it should do an element copy
for small structs.

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