[Issue 23279] Segmentation fault on mixin template + using unknown type

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23279

--- Comment #4 from RazvanN <razvan.nitu1305 at gmail.com> ---
It seems like `__traits(hasMember)` gets confused by the forward reference.
Putting the `traits(hasMember)` it after the declaration of `setIt` does not
result in an ice.

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