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/mem_map.cc b/runtime/mem_map.cc
index c118471..51aba9c 100644
--- a/runtime/mem_map.cc
+++ b/runtime/mem_map.cc
@@ -238,6 +238,9 @@
 
 MemMap* MemMap::MapAnonymous(const char* name, uint8_t* expected_ptr, size_t byte_count, int prot,
                              bool low_4gb, std::string* error_msg) {
+#ifndef __LP64__
+  UNUSED(low_4gb);
+#endif
   if (byte_count == 0) {
     return new MemMap(name, nullptr, 0, nullptr, 0, prot, false);
   }