Various fixes related to integer negate operations.

- Emit an RSB instruction for HNeg nodes in the ARM code
  generator instead of RSBS, as we do not need to update the
  condition code flags in this case.
- Simply punt when trying to statically evaluate a long
  unary operation, instead of aborting.
- Move a test case to the right place.

Change-Id: I35eb8dea58ed35258d4d8df77181159c3ab07b6f