Hi JB,
The libxml2 distribution comes with a Visual Studio project which for libxml2-2.9.1 can be found in the folder \libxml2-2.9.1\win32\VC10\libxml2.sln. This project is configured only for Win32, but a new configuration for x64 can be easily added by opening Configuration Manager, select Active solution platform -> <New...> and choose x64 instead of ARM. One more thing that needs to be done is to set the project type as dll, this is done from the project's properties window, Configuration Properties -> General -> Configuration type. After doing this add the ws2_32.lib to the Linker -> Input -> Additional Dependencies. Also you need to comment the '#define LIBXML_ICONV_ENABLED' from xmlversion.h. That's it, after this you should be able to build a 64 bit version of libxml2.
Regarding 'AD9361_iiostream.c' I have never tried to build it under Windows. We'll have a look into this and let you know.
Regards,
Andrei