Fix all our unused parameter warnings so we let GCC report them.

There were a couple of genuine bugs here (fixed), plus there's a missing
feature in trace.cc that I've just added a TODO for.

Also note that I haven't touched the compilers; this warning is still
explicitly disabled for that code. I'll do that when there's less going
on in those directories.

Change-Id: Ic3570bf82411a07c7530bfaf1995ac995b9fc00f
diff --git a/src/hprof/hprof.cc b/src/hprof/hprof.cc
index 6de9c64..04e43d2 100644
--- a/src/hprof/hprof.cc
+++ b/src/hprof/hprof.cc
@@ -278,7 +278,7 @@
   return err;
 }
 
-int Hprof::StackTraceSerialNumber(const void *obj) {
+int Hprof::StackTraceSerialNumber(const void* /*obj*/) {
   return HPROF_NULL_STACK_TRACE;
 }