Add missing 'override'.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@243773 91177308-0d34-0410-b5e6-96231b3b80d8

clang-tidy/misc/UnusedAliasDeclsCheck.h

@@ -22,7 +22,7 @@ public:
       : ClangTidyCheck(Name, Context) {}
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
-  void onEndOfTranslationUnit();
+  void onEndOfTranslationUnit() override;
 
 private:
   llvm::DenseMap<const Decl *, CharSourceRange> FoundDecls;