[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 #7 from FeepingCreature <default_357-line at yahoo.de> ---
Unified with what I'm learning from the testcase from 21235:

```
// gag the foo error
static assert(!__traits(compiles, foo()));

void foo()() {
    static assert(false);
    bar!();
}

// foo() is not errored while bar compiles? because circular
void bar()() { foo(); }

// no error
void main() { bar(); }
```

I don't think we'll get it smaller than this.

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