[Issue 20442] Please add a warning that will complain about unused imports

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20442

--- Comment #2 from Manu <turkeyman at gmail.com> ---
That's a shit solution.
Build systems are way complex enough, and a whole other pass to make a trivial
warning is silly when we already have a perfectly good warning solution; `-w`

--