ART: Add Clang's -Wused-but-marked-unused

Add detection of wrong unused annotations. Fix our codebase.

Change-Id: I85cc20f2eac71c1ec6c5c7cd6efb08454a629634
diff --git a/compiler/optimizing/intrinsics_arm.cc b/compiler/optimizing/intrinsics_arm.cc
index 33176f0..94e27e9 100644
--- a/compiler/optimizing/intrinsics_arm.cc
+++ b/compiler/optimizing/intrinsics_arm.cc
@@ -776,10 +776,10 @@
   __ mov(out, ShifterOperand(0), CC);
 }
 
-void IntrinsicLocationsBuilderARM::VisitUnsafeCASInt(HInvoke* invoke ATTRIBUTE_UNUSED) {
+void IntrinsicLocationsBuilderARM::VisitUnsafeCASInt(HInvoke* invoke) {
   CreateIntIntIntIntIntToIntPlusTemps(arena_, invoke);
 }
-void IntrinsicLocationsBuilderARM::VisitUnsafeCASObject(HInvoke* invoke ATTRIBUTE_UNUSED) {
+void IntrinsicLocationsBuilderARM::VisitUnsafeCASObject(HInvoke* invoke) {
   CreateIntIntIntIntIntToIntPlusTemps(arena_, invoke);
 }
 void IntrinsicCodeGeneratorARM::VisitUnsafeCASInt(HInvoke* invoke) {