Remove -Wno-unused-parameter and -Wno-sign-promo from base cflags.

Fix associated errors about unused paramenters and implict sign conversions.
For sign conversion this was largely in the area of enums, so add ostream
operators for the effected enums and fix tools/generate-operator-out.py.
Tidy arena allocation code and arena allocated data types, rather than fixing
new and delete operators.
Remove dead code.

Change-Id: I5b433e722d2f75baacfacae4d32aef4a828bfe1b
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index 861a182..2fd5a52 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -265,7 +265,7 @@
   return true;
 }
 
-void ImageWriter::ComputeEagerResolvedStringsCallback(Object* obj, void* arg) {
+void ImageWriter::ComputeEagerResolvedStringsCallback(Object* obj, void* arg ATTRIBUTE_UNUSED) {
   if (!obj->GetClass()->IsStringClass()) {
     return;
   }
@@ -661,7 +661,8 @@
     }
   }
 
-  void operator()(mirror::Class* /*klass*/, mirror::Reference* ref) const
+  void operator()(mirror::Class* klass ATTRIBUTE_UNUSED,
+                  mirror::Reference* ref ATTRIBUTE_UNUSED) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) {
     LOG(FATAL) << "Reference not expected here.";