Host and target architectures need to have the same pointer size.
When building on x86_64, do not force 32-bit host binaries if the target
architecture is also 64-bit.

See http://luajit.org/install.html#cross

Add 64-bit arm (aarch64) to the list of architectures.

Signed-off-by: Eric Kinzie <ekinzie@labn.net>