Use Consistent Qt style for ifdef

[ann0see]

Are the Windows and Android ones okay? Is the Q_ a "Qt" thing that we can use for all platforms? What's the OT_ thing?

Originally posted by @pljones in #3360 (comment)

The code should be refactored such that only one style is used. Probably Q_OS_WIN: https://doc.qt.io/qt-5/qtglobal.html#Q_OS_WIN

[softins]

The OT_ thing is just an enum within the Jamulus code, for the protocol byte that indicates the OS type:

jamulus/src/util.h

Lines 1062 to 1074 in d6c6fc7

	class COSUtil
	{
	public:
	enum EOpSystemType
	{
	// used for protocol -> enum values must be fixed!
	OT_WINDOWS = 0,
	OT_MAC_OS = 1,
	OT_LINUX = 2,
	OT_ANDROID = 3,
	OT_I_OS = 4,
	OT_UNIX = 5
	};

[ann0see]

Yes, I commented that in the respective PR.