testFilename in std.stdio

[Rogni]

Hi everyone.
I have a file main.d

```
import std.stdio: writeln;
int main (string []) { return 0; }
```

When I try to get depend files with command `ldc2 main.d 
--unittest --deps=main.deps --o-` such errors are received:

```
/home/mak/progs/ldc2-1.26.0-linux-x86_64/bin/../import/std/stdio.d(563): Error: undefined identifier `testFilename`
/home/mak/progs/ldc2-1.26.0-linux-x86_64/bin/../import/std/stdio.d(759): Error: undefined identifier `testFilename`
/home/mak/progs/ldc2-1.26.0-linux-x86_64/bin/../import/std/stdio.d(765): Error: undefined identifier `testFilename`
/home/mak/progs/ldc2-1.26.0-linux-x86_64/bin/../import/std/stdio.d(781): Error: undefined identifier `testFilename`
...
```

Is it possible that the std/stdio.d function 
[`testFilename`](https://github.com/dlang/phobos/blob/adff6577b9fd5f512ec348494e8037a0bb71b89f/std/stdio.d#L5908) wrapped in `version (StdUnittest)` is in version (unittest) ?

version of ldc - 1.26.0