fix windows code to build with MSVC

- remove __attribute__((unused)) not supported on MSVC
- remove  __attribute((unused)) not supported on MSVC
- add symbol exports to RemoteDataReadQueue and RemoteDataQueue
- add export symbols to sdrsrv

plugins/samplesource/soapysdrinput/soapysdrinputplugin.cpp

@@ -90,9 +90,9 @@ PluginInterface::SamplingDevices SoapySDRInputPlugin::enumSampleSources()
 
 #ifdef SERVER_MODE
 PluginInstanceGUI* SoapySDRInputPlugin::createSampleSourcePluginInstanceGUI(
-        const QString& sourceId __attribute__((unused)),
-        QWidget **widget __attribute__((unused)),
-        DeviceUISet *deviceUISet __attribute__((unused)))
+        const QString& sourceId,
+        QWidget **widget,
+        DeviceUISet *deviceUISet)
 {
     return 0;
 }