[gardening] C++ gardening: Terminate namespaces, fix argument names, ...

Changes:
* Terminate all namespaces with the correct closing comment.
* Make sure argument names in comments match the corresponding parameter name.
* Remove redundant get() calls on smart pointers.
* Prefer using "override" or "final" instead of "virtual". Remove "virtual" where appropriate.

lib/SILOptimizer/Transforms/Sink.cpp

@@ -162,7 +162,7 @@ public:
     return "Sinks instructions closer to their users";
   }
 };
-}
+} // end anonymous namespace
 
 SILTransform *swift::createCodeSinking() {
   return new CodeSinkingPass();