Optimize suspend checks in optimizing compiler.

- Remove the ones added during graph build (they were added
  for the baseline code generator).
- Emit them at loop back edges after phi moves, so that the test
  can directly jump to the loop header.
- Fix x86 and x86_64 suspend check by using cmpw instead of cmpl.

Change-Id: I6fad5795a55705d86c9e1cb85bf5d63dadfafa2a
diff --git a/compiler/optimizing/code_generator_x86.h b/compiler/optimizing/code_generator_x86.h
index ffcaf60..23145bf 100644
--- a/compiler/optimizing/code_generator_x86.h
+++ b/compiler/optimizing/code_generator_x86.h
@@ -119,6 +119,11 @@
   X86Assembler* GetAssembler() const { return assembler_; }
 
  private:
+  // Generate code for the given suspend check. If not null, `successor`
+  // is the block to branch to if the suspend check is not needed, and after
+  // the suspend call.
+  void GenerateSuspendCheck(HSuspendCheck* check, HBasicBlock* successor);
+
   X86Assembler* const assembler_;
   CodeGeneratorX86* const codegen_;