[Issue 19091] __traits(compiles) and error in templated structs leads to missing symbol

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19091

--- Comment #14 from FeepingCreature <default_357-line at yahoo.de> ---
Hm, this one seems to be distinctive enough that I should report it as a new
one.

Sorry, it smelled familiar. But the assert seems its own problem site. Re-filed
as https://issues.dlang.org/show_bug.cgi?id=22917

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