Implement int negate instruction in the optimizing compiler.

- Add support for the neg-int (integer two's complement
  negate) instruction in the optimizing compiler.
- Add a HNeg node type for control-flow graphs and an
  intermediate HUnaryOperation base class.
- Generate ARM, x86 and x86-64 code for integer HNeg nodes.

Change-Id: I72fd3e1e5311a75c38a8cb665a9211a20325a42e
7 files changed