[Issue 17878] Add __traits(isFuture, ...)

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=17878

--- Comment #1 from RazvanN <razvan.nitu1305 at gmail.com> ---
PR : https://github.com/dlang/dmd/pull/7232

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