Fixed build

@irungentoo, you can ask people to revise their code to follow the [Coding Style](https://github.com/irungentoo/ProjectTox-Core/wiki/Coding-Style) and also ask them to include source files in cmake files to make sure their pull request builds.

Do we even need the `helper.c`?

Also, experimental branch is so far behind the master, that I had to add the 23f13cd95d5d9afaadd859a4d256986817e613b9 fix here.