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/optimizing/code_generator_arm64.h b/compiler/optimizing/code_generator_arm64.h
index a4003ff..5530f46 100644
--- a/compiler/optimizing/code_generator_arm64.h
+++ b/compiler/optimizing/code_generator_arm64.h
@@ -180,11 +180,15 @@
   virtual Location GetStackLocation(HLoadLocal* load) const OVERRIDE;
 
   virtual size_t SaveCoreRegister(size_t stack_index, uint32_t reg_id) OVERRIDE {
+    UNUSED(stack_index);
+    UNUSED(reg_id);
     UNIMPLEMENTED(INFO) << "TODO: SaveCoreRegister";
     return 0;
   }
 
   virtual size_t RestoreCoreRegister(size_t stack_index, uint32_t reg_id) OVERRIDE {
+    UNUSED(stack_index);
+    UNUSED(reg_id);
     UNIMPLEMENTED(INFO) << "TODO: RestoreCoreRegister";
     return 0;
   }