wlroots headers can mostly be included with extern "C" blocks. Two
exceptions are the use of `static` for array args and `class` as a
struct field. These can be #define'ed to avoid C++ build errors.
This allows the whole project to be built as a single C++ codebase,
without having to maintain hybrid header files.
For now just mark one repaint per refresh interval without any particular
alignment, as that can be hard to get in nested. We'll use the display
timing extensions for that later.
We'll have it align properly in embedded mode soon.
