ART: Make the dominator bitvectors expandable

The dominator based bitvectors are not expandable. However, if we wish
 to add BasicBlocks and recalculate, it is required to make them expandable.

Change-Id: I250684783c233eca31bb40a5bc971c97fcf7c42d
Signed-off-by: Jean Christophe Beyler <jean.christophe.beyler@intel.com>