[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/SIL/SILFunction.cpp

@@ -466,7 +466,7 @@ struct DOTGraphTraits<SILFunction *> : public DefaultDOTGraphTraits {
     return "";
   }
 };
-} // end llvm namespace
+} // namespace llvm
 #endif
 
 #ifndef NDEBUG