[Issue 18239] std.experimental.allocator fillWithMemcpy could use memset/wmemset for T.sizeof==1 or wint_t.sizeof

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18239

--- Comment #1 from Nathan S. <n8sh.secondary at hotmail.com> ---
Could also use wmemset when T.sizeof == wint_t.sizeof

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