Apply clang-tidy fixes for modernize-use-override in SerializeToLLVMBitcode.cpp (NFC)

Author: joker-eph

mlir/unittests/Target/LLVM/SerializeToLLVMBitcode.cpp

@@ -32,7 +32,7 @@ using namespace mlir;
 
 class MLIRTargetLLVM : public ::testing::Test {
 protected:
-  virtual void SetUp() {
+  void SetUp() override {
     llvm::InitializeNativeTarget();
     llvm::InitializeNativeTargetAsmPrinter();
   }