Use ATTRIBUTE_UNUSED more.

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

Change-Id: If247dce58b72056f6eea84968e7196f0b5bef4da
diff --git a/runtime/base/debug_stack.h b/runtime/base/debug_stack.h
index 03f4575..e19aecb 100644
--- a/runtime/base/debug_stack.h
+++ b/runtime/base/debug_stack.h
@@ -54,7 +54,7 @@
 template <>
 class DebugStackReferenceImpl<false> {
  public:
-  explicit DebugStackReferenceImpl(DebugStackRefCounterImpl<false>* counter) { UNUSED(counter); }
+  explicit DebugStackReferenceImpl(DebugStackRefCounterImpl<false>* counter ATTRIBUTE_UNUSED) {}
   DebugStackReferenceImpl(const DebugStackReferenceImpl& other) = default;
   DebugStackReferenceImpl& operator=(const DebugStackReferenceImpl& other) = default;
   void CheckTop() { }
@@ -63,7 +63,7 @@
 template <>
 class DebugStackIndirectTopRefImpl<false> {
  public:
-  explicit DebugStackIndirectTopRefImpl(DebugStackReferenceImpl<false>* ref) { UNUSED(ref); }
+  explicit DebugStackIndirectTopRefImpl(DebugStackReferenceImpl<false>* ref ATTRIBUTE_UNUSED) {}
   DebugStackIndirectTopRefImpl(const DebugStackIndirectTopRefImpl& other) = default;
   DebugStackIndirectTopRefImpl& operator=(const DebugStackIndirectTopRefImpl& other) = default;
   void CheckTop() { }