[clang][NFC] Add a missing 'override'

Author: kepler-5

clang/unittests/CrossTU/CrossTranslationUnitTest.cpp

@@ -29,7 +29,7 @@ class CTUASTConsumer : public clang::ASTConsumer {
   explicit CTUASTConsumer(clang::CompilerInstance &CI, bool *Success)
       : CTU(CI), Success(Success) {}
 
-  void HandleTranslationUnit(ASTContext &Ctx) {
+  void HandleTranslationUnit(ASTContext &Ctx) override {
     auto FindFInTU = [](const TranslationUnitDecl *TU) {
       const FunctionDecl *FD = nullptr;
       for (const Decl *D : TU->decls()) {