Can't locally build javasphinx on OS X (also windows and linux w/o certain packages)

We currently build a custom version of javasphinx as part of our spxhinx configuration, but to build it we need C compilers and the right libraries installed. Doing this in a portable way is hard and (at least on my Mac) failed because libxml2 wasn't installed.

For now, this patch checks if javasphinx is avialable and doesn't use it if it's not:
https://git.opendaylight.org/gerrit/#/c/41580/

In the long-run it would be better if it was available cross-platform.