Add vbnc support

Although it seems vbnc is not well supported, people use it.
Note: vbnc (.net 4.0) shipped with "mono-vbnc 2.10-2" on Debian
does not work and seems hard to fix with command line arguments.
Use "stable" vbnc2 (.net 2.0) instead.
Add gcj config

gcj has much less start time than javac.