avoid build error in visual studio 2010 also

The problem fixed by #210 on VS 2013 also exists on VS2010. This makes it work at least with 64-bit targets on 2010; I don't have 2012, but I would imagine it's the same there, so I had it check for both of those.

I'm not sure about 32-bit targets; someone more knowledgeable about Visual Studio might be able to determine what instances this is and isn't necessary in.