Set vtable in class object to null after linking.

This is follow-up work of embedding imt and vtable for
faster interface/virtual call dispatching.
Once vtable becomes embedded, the original vtable is nulled.

(cherry picked from commit 2cdbad7c62f126581ec5177104de961c4d71adaa)

Change-Id: I6acdcd1ee560d387fb77c55c58bbe3598c197ba1
11 files changed