Shrink the size of the final binary. If it is too large it will have problem executi...

Shrink the size of the final binary.  If it is too large it will have problem executing on Tilera.  We compress the virtual dispatch table: we use one row to represent the methods defined in interfaces that have the same prototype; and we do not generate colums for interfaces as there can not be instances of interfaces.  Moreover, we do not generate methods that are never invoked.