Use code also for other unix systems like BSD (#507)

src/FloatingDragPreview.cpp

@@ -262,7 +262,7 @@ CFloatingDragPreview::CFloatingDragPreview(QWidget* Content, QWidget* parent) :
 		setAttribute(Qt::WA_TranslucentBackground);
 	}
 
-#ifdef Q_OS_LINUX
+#if defined(Q_OS_UNIX) && !defined(Q_OS_MACOS)
     auto Flags = windowFlags();
     Flags |= Qt::WindowStaysOnTopHint | Qt::X11BypassWindowManagerHint;
     setWindowFlags(Flags);