[Issue 21740] Typeof mixin regression with v2.096

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21740

--- Comment #2 from kinke <kinke at gmx.net> ---
Thx for digging. Just in case, the problem isn't the pragma(msg), but that
`static assert(!is(typeof(mixin(foo()))));` newly fails.

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