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/monitor_pool.h b/runtime/monitor_pool.h
index 5b92093..27678dc 100644
--- a/runtime/monitor_pool.h
+++ b/runtime/monitor_pool.h
@@ -53,6 +53,7 @@
 
   static void ReleaseMonitor(Thread* self, Monitor* monitor) {
 #ifndef __LP64__
+    UNUSED(self);
     delete monitor;
 #else
     GetMonitorPool()->ReleaseMonitorToPool(self, monitor);
@@ -61,6 +62,7 @@
 
   static void ReleaseMonitors(Thread* self, MonitorList::Monitors* monitors) {
 #ifndef __LP64__
+    UNUSED(self);
     STLDeleteElements(monitors);
 #else
     GetMonitorPool()->ReleaseMonitorsToPool(self, monitors);
@@ -85,6 +87,7 @@
 
   static MonitorId ComputeMonitorId(Monitor* mon, Thread* self) {
 #ifndef __LP64__
+    UNUSED(self);
     return MonitorIdFromMonitor(mon);
 #else
     return GetMonitorPool()->ComputeMonitorIdInPool(mon, self);