Fix build with latest wlroots, dbus libs

[depau]

I tried to make commits self-explanatory.

Notice that this is my first time dealing with C++ code, so please do review :)

[topisani]

Thanks, this looks good!

I'd prefer it if it could build with the chromium dbusc++ fork, since that's a lot less buggy than the mainline, but then maybe we should add that as a submodule.

It's been some time since I've worked on this, but I still use cloth-notifications, cloth-outputs and cloth-lock on a daily basis, so I appreciate the help.

Tell me when you are done with your patches, and I'll merge it

[depau]

I noticed mainline dbus-c++ generated code doesn't build with Clang for reasons that are beyond my knoweledge, does chromium's?

Anyway it should be pretty much good with these patches, next week I'll do some more work and eventually switch to it, if you want to merge it it's fine, I'll open a new PR if needed :)