Asynchronous shader compilation

[ghost]

Would it be possible to add an asynchronous(skip drawing) shader compilation method similar to dolphin emulator? (removes shader compilation stutters at the cost of slightly late rendering).

[gonetz]

@Nejsplitter and anyone else with shader compilation stuttering problem: could you compare build from #2775 with regular build from master? Does it help with the problem anyhow? The fix works only if "threaded video" option is enabled, so you may turn it on/off to see the difference.