Use ATTRIBUTE_UNUSED more.

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

Change-Id: If247dce58b72056f6eea84968e7196f0b5bef4da
diff --git a/runtime/fault_handler.cc b/runtime/fault_handler.cc
index 30a0983..5b31b3a 100644
--- a/runtime/fault_handler.cc
+++ b/runtime/fault_handler.cc
@@ -406,9 +406,8 @@
   manager_->AddHandler(this, false);
 }
 
-bool JavaStackTraceHandler::Action(int sig, siginfo_t* siginfo, void* context) {
+bool JavaStackTraceHandler::Action(int sig ATTRIBUTE_UNUSED, siginfo_t* siginfo, void* context) {
   // Make sure that we are in the generated code, but we may not have a dex pc.
-  UNUSED(sig);
 #ifdef TEST_NESTED_SIGNAL
   bool in_generated_code = true;
 #else