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/runtime/gc/accounting/mod_union_table.cc b/runtime/gc/accounting/mod_union_table.cc
index 753b42d..0a15e9e 100644
--- a/runtime/gc/accounting/mod_union_table.cc
+++ b/runtime/gc/accounting/mod_union_table.cc
@@ -46,6 +46,7 @@
   }
 
   inline void operator()(uint8_t* card, uint8_t expected_value, uint8_t new_value) const {
+    UNUSED(new_value);
     if (expected_value == CardTable::kCardDirty) {
       cleared_cards_->insert(card);
     }
@@ -62,6 +63,7 @@
   }
 
   void operator()(uint8_t* card, uint8_t expected_card, uint8_t new_card) const {
+    UNUSED(new_card);
     if (expected_card == CardTable::kCardDirty) {
       cleared_cards_->push_back(card);
     }