[IR] Fixed another depth issue for %block (in module/instance evals).

* Account for the extra dynamic scope inserted by the runtime for
  module/instance evals while generting scope depths for %block
  in the IR builder.

* Eliminates all errors from MRI tests. Latest status (vis-a-vis
  -X-C failures):
  - 2 failures left for test/*
  - 10 failures left for test/mri/*