Threaded shader compilation

[siro20]

Most games create shaders on startup. WINE compiles them at time of first use (due to OpenGL backend), but nine compiles them at creation. While I prefer nine behaviour to reduce FPS drop due to long (up to 500msec) shader compilation, I would like to see them happen on a seperate thread. The shaders would be compiled in the background and the main thread has to wait for compilation if the shader used in a draw call hasn't been compiled yet. As another improvement the compiling thread should be signaled on which shader the main thread is waiting for and compile it first.