In order to use gcj to compile the java binding, you must also have development
files of libgcj.  On Debian systems that translates to:

 - gcj 3.3 -> libgcj4-dev
 - gcj 3.4 -> libgcj5-dev
 - gcj 4.0 -> libgcj6-dev
 - gcj 4.1 -> libgcj7-dev