Build has too many warnings

[Enerccio]

Low priority issue, but if you are building a lot, it is pretty crappy.

Most of it is inside chck submodule, but some are inside wlc itself, like in xdg_cb_popup_grab by @kozec

[Earnestly]

They're pretty much all non null warnings because the compiler isn't smart enough, making the warning mechanism chck added fairly pointless. It's all rather unfortunate.

[Cloudef]

https://github.com/Cloudef/wlc/commit/32dfed15b74f28e77bc4170ef72f22c3542e71be should fix them