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/runtime_linux.cc b/src/runtime_linux.cc
index d7b32ee..a604819 100644
--- a/src/runtime_linux.cc
+++ b/src/runtime_linux.cc
@@ -41,7 +41,7 @@
   return mangled_name + "()";
 }
 
-void Runtime::PlatformAbort(const char* file, int line) {
+void Runtime::PlatformAbort(const char* /*file*/, int /*line_number*/) {
   // On the host, we don't have debuggerd to dump a stack for us.
 
   // Get the raw stack frames.