[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/SILCoverageMap.cpp

@@ -90,7 +90,7 @@ struct Printer {
     return OS;
   }
 };
-}
+} // end anonymous namespace
 
 void SILCoverageMap::printCounter(llvm::raw_ostream &OS,
                                   llvm::coverage::Counter C) const {