Disable build for WinRT

According to MSDN Windows Store apps will not have any
serial port replacement.

http://msdn.microsoft.com/en-us/library/windows/apps/hh464945.aspx

Change-Id: I2aa54462c411341e3b3cdbbbf65a7b3397df93b6
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>