message: Fix Toy tutorial gcc 7 build (NFC)
diff: @@ -112,12 +112,6 @@ private:
  /// scope is destroyed and the mappings created in this scope are dropped.
  llvm::ScopedHashTable<StringRef, mlir::Value *> symbolTable;
  - /// Create a new scope in the symbol table. The scope lifetime is managed by
  - /// the returned RAII object.
  - ScopedHashTableScope<llvm::StringRef, mlir::Value *> create_scope() {
  - return ScopedHashTableScope<llvm::StringRef, mlir::Value *>(symbolTable);
  - }
  -
  /// Helper conversion for a Toy AST location to an MLIR location.
  mlir::FileLineColLoc loc(Location loc) {
  return mlir::FileLineColLoc::get(
  @@ -158,7 +152,7 @@ private:
  /// Emit a new function and add it to the MLIR module.
  std::unique_ptr<mlir::Function> mlirGen(FunctionAST &funcAST) {
  // Create a scope in the symbol table to hold variable declarations.
  - auto var_scope = create_scope();
  + ScopedHashTableScope<llvm::StringRef, mlir::Value *> var_scope(symbolTable);
  // Create an MLIR function for the given prototype.
  std::unique_ptr<mlir::Function> function(mlirGen(*funcAST.getProto()));
  @@ -457,7 +451,7 @@ private:
  /// Codegen a list of expression, return false if one of them hit an error.
  bool mlirGen(ExprASTList &blockAST) {
  - auto var_scope = create_scope();
  + ScopedHashTableScope<llvm::StringRef, mlir::Value *> var_scope(symbolTable);
  for (auto &expr : blockAST) {
  // Specific handling for variable declarations, return statement, and
  // print. These can only appear in block list and not in nested
  