Building libxml2-2.9.2 for iOS 64 bit

Question

So far I was building libxml2-2.9.2 and previous versions for iOS 32 bits only. The command I'm using to call configuration script is:

./configure --with-debug=no --host=arm-apple-darwin12.5.0 --with-iconv=no --with-zlib=no

and this was working just fine.

Now to build it for 64 bit architecture I'm passing:

./configure --with-debug=no --host=arm64-apple-darwin12.5.0 --with-iconv=no --with-zlib=no

And this is printing out the following errors:

checking build system type... x86_64-apple-darwin12.5.0
checking host system type... Invalid configuration `arm64-apple-darwin12.5.0': machine `arm64-apple' not recognized
configure: error: /bin/sh ./config.sub arm64-apple-darwin12.5.0 failed

Do you know how to fix this problem? Thanks in advance.