[llvm-opt-fuzzer] Skip creating/initializing legacy PM passes

[bjope]

Summary

Afaict llvm-opt-fuzzer is using the new pass manager. So there
shouldn't be a need to create/initialize/register the legacy PM
version of passes.

[nikic]

LG

llvm/tools/llvm-opt-fuzzer/llvm-opt-fuzzer.cpp

 //===--- llvm-opt-fuzzer.cpp - Fuzzer for instruction selection ----------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // Tool to fuzz optimization passes using libFuzzer.
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/Bitcode/BitcodeWriter.h"
 #include "llvm/CodeGen/CommandFlags.h"
 #include "llvm/FuzzMutate/FuzzerCLI.h"
 #include "llvm/FuzzMutate/IRMutator.h"
 #include "llvm/IR/Verifier.h"
-#include "llvm/InitializePasses.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Target/TargetMachine.h"
 
 using namespace llvm;
extern "C" LLVM_ATTRIBUTE_USED int LLVMFuzzerInitialize(
   install_fatal_error_handler(handleLLVMFatalError, nullptr);
 
   // Initialize llvm
   //
 
   InitializeAllTargets();
   InitializeAllTargetMCs();
 
-  PassRegistry &Registry = *PassRegistry::getPassRegistry();
-  initializeCore(Registry);
-  initializeScalarOpts(Registry);
-  initializeVectorization(Registry);
-  initializeIPO(Registry);
-  initializeAnalysis(Registry);
-  initializeTransformUtils(Registry);
-  initializeInstCombine(Registry);
-  initializeTarget(Registry);
-
   // Parse input options
   //
 
   handleExecNameEncodedOptimizerOpts(*argv[0]);
   parseFuzzerCLOpts(*argc, *argv);
 
   // Create TargetMachine
   //