[Issue 20717] Unsilenced bogus "undefined identifier" error from speculative collision

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20717

--- Comment #1 from Basile-z <b2.temp at gmx.com> ---
The problem is that the semantic of the alias is run at the wrong time, i.e the
error are not gagged but in the present context they should. The gagging is
activated when the IsExp is visited. But the alias sema is run when the
overload is inserted.

--