Revert "Revert "Introduce a NearLabel in thumb2.""

This reverts commit 1f277e3c.

- Fix CompareAndBranch to not use cbz/cbnz with high registers.
- Add a test for CompareAndBranch with the *inc file, as the
  other assembler test infrastructure does not handle labels.

Change-Id: If552bf1112b96caa3b9bb6c73c4b40bb90a33db7