debugger: avoid member data initializers unsupported by MSVC
cmake: add compiler version check for MSVC
qt4apps: Marx2DGraph: ugly MSVC compile fix

Better would be not to use M_PI at all, for portability.
core: MarControl: export operator overload symbols
realtime: export Runner and Control classes
realtime: Runner: raise ticking thread priority on Windows
marsystems: AudioSink: apply useful RtAudio options

* Always try to use real-time priority for RtAudio callback thread.
* In "realtime" mode, let RtAudio minimize buffering for lowest latency.