Add CFG and SSA form checkers in the optimizing compiler.

Checks performed on control-flow graphs:
- Ensure that the predecessors and successors of a basic block are
  consistent within a control-flow graph.
- Ensure basic blocks end with a branch instruction.
- Detect phi functions listed in non-phi instruction lists and vice
  versa.
- Ensure a block's instructions (and phi functions) are associated
  with this very block.

Checks performed on SSA form graphs:
- Ensure an instruction dominates all its uses.
- Ensure there are no critical edges.

Change-Id: I1c12b4a61ecf608682152c897980ababa7eca847