how do I activate contracts for phobos functions in dmd

[Stefan Koch]

On Friday, 2 November 2018 at 14:10:35 UTC, Richard Palme wrote:
> My guess is that I have to build phobos with:
>
> $make -f posix.mak BUILD=debug
>
> but then what do I do next? I'm using Linux and I built 
> dmd+phobos manually by following this guide: 
> https://wiki.dlang.org/Building_under_Posix

Which phobos functions are used in dmd?
there _should_ be none!