Enable building 64-bit binaries using VS2013 Express

RT-38475 enabled building with Visual Studio 2012 and 2013 in addition to the default VS 2010. Microsoft has added support in the Express versions of the compiler (starting with VS 2012 I think) to build 64-bit binaries using Visual Studio Express. We need some small changes to the build to detect that we are using Express and change some of the include and lib paths from "amd64" to "x86_amd64" in a couple of places.