[Clang-tidy] Fix Clang-tidy modernize-use-override warning in unittests/clang-tidy/IncludeInserterTest.cpp; other minor fixes

[Eugene.Zelenko]

Summary

I checked this patch on my own build on RHEL 6. Regressions were OK.

[aaron.ballman]

LGTM!

[alexfh]

unittests/clang-tidy/IncludeInserterTest.cpp

101

I'd better remove it completely.

[Eugene.Zelenko]

unittests/clang-tidy/IncludeInserterTest.cpp

101

Will do this in commit.

unittests/clang-tidy/IncludeInserterTest.cpp

 public:
   CXXSystemIncludeInserterCheck(StringRef CheckName, ClangTidyContext *Context)
       : IncludeInserterCheckBase(CheckName, Context) {}
-  virtual ~CXXSystemIncludeInserterCheck() {}
+  ~CXXSystemIncludeInserterCheck() override = default;
 
   std::vector<StringRef> HeadersToInclude() const override { return {"set"}; }
   bool IsAngledInclude() const override { return true; }

                                    "insert_includes_test_header.cc"));
 }
 
-} // namespace
+} // anonymous namespace
 } // namespace tidy
 } // namespace clang