Use ATTRIBUTE_UNUSED more.

Use it in lieu of UNUSED(), which had some incorrect uses.

Change-Id: If247dce58b72056f6eea84968e7196f0b5bef4da
diff --git a/compiler/dex/pass.h b/compiler/dex/pass.h
index 0def056..16414ef 100644
--- a/compiler/dex/pass.h
+++ b/compiler/dex/pass.h
@@ -53,10 +53,7 @@
    * @param data the PassDataHolder.
    * @return whether or not to execute the pass.
    */
-  virtual bool Gate(const PassDataHolder* data) const {
-    // Unused parameter.
-    UNUSED(data);
-
+  virtual bool Gate(const PassDataHolder* data ATTRIBUTE_UNUSED) const {
     // Base class says yes.
     return true;
   }
@@ -64,17 +61,13 @@
   /**
    * @brief Start of the pass: called before the Worker function.
    */
-  virtual void Start(PassDataHolder* data) const {
-    // Unused parameter.
-    UNUSED(data);
+  virtual void Start(PassDataHolder* data ATTRIBUTE_UNUSED) const {
   }
 
   /**
    * @brief End of the pass: called after the WalkBasicBlocks function.
    */
-  virtual void End(PassDataHolder* data) const {
-    // Unused parameter.
-    UNUSED(data);
+  virtual void End(PassDataHolder* data ATTRIBUTE_UNUSED) const {
   }
 
   /**