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/jni_internal.cc b/runtime/jni_internal.cc
index ad06b85..dd66af7 100644
--- a/runtime/jni_internal.cc
+++ b/runtime/jni_internal.cc
@@ -1749,6 +1749,7 @@
   }
 
   static void ReleaseStringCritical(JNIEnv* env, jstring java_string, const jchar* chars) {
+    UNUSED(chars);
     CHECK_NON_NULL_ARGUMENT_RETURN_VOID(java_string);
     ScopedObjectAccess soa(env);
     gc::Heap* heap = Runtime::Current()->GetHeap();
@@ -1777,7 +1778,7 @@
     return bytes;
   }
 
-  static void ReleaseStringUTFChars(JNIEnv* env, jstring, const char* chars) {
+  static void ReleaseStringUTFChars(JNIEnv*, jstring, const char* chars) {
     delete[] chars;
   }