[mlir][NFC] Add missing include guards to MlirOptMain.h

[ftynse]

I think we are using _ for / int the pass, but not to separate words, so we'll have MLIR_SUPPORT_MLIROPTMAIN_H even if it doesn't read nicely.

[mehdi_amini]

LG with fixing the wording as Alex suggests (and clang-tidy flags)

[vinograd47]

Fixed include guard macro name to match preferred style.
Rebased on latest main branch.

[vinograd47]

@mehdi_amini I don't have commit access to the repo. Could you please land the change by yourself?

mlir/include/mlir/Support/MlirOptMain.h

 //===- MlirOptMain.h - MLIR Optimizer Driver main ---------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // Main entry function for mlir-opt for when built as standalone binary.
 //
 //===----------------------------------------------------------------------===//
 
+#ifndef MLIR_SUPPORT_MLIROPTMAIN_H
+#define MLIR_SUPPORT_MLIROPTMAIN_H
+
 #include "mlir/Support/LogicalResult.h"
 #include "llvm/ADT/StringRef.h"
 
 #include <memory>
 
 namespace llvm {
 class raw_ostream;
 class MemoryBuffer;

 /// - preloadDialectsInContext will trigger the upfront loading of all
 ///   dialects from the global registry in the MLIRContext. This option is
 ///   deprecated and will be removed soon.
 LogicalResult MlirOptMain(int argc, char **argv, llvm::StringRef toolName,
                           DialectRegistry &registry,
                           bool preloadDialectsInContext = true);
 
 } // end namespace mlir
+
+#endif // MLIR_SUPPORT_MLIROPTMAIN_H