[llvm] [llvm-objdump] Support --mcpu=help/--mattr=help without -d (PR #165661)

[Ruoyu Qiu via llvm-commits]

cabbaken wrote:

I have added some test cases and fix the behavior of 'mcpu=help + --triple' (won't emit error anymore). 
I think you may have any thoughts on this approach (Because it looks a bit inelegant)
```
  const bool PrintCpuHelp = (MCPU == "help" || is_contained(MAttrs, "help"));

  const bool ShouldDump =
      ArchiveHeaders || Disassemble || DwarfDumpType != DIDT_Null ||
      DynamicRelocations || FileHeaders || PrivateHeaders || RawClangAST ||
      Relocations || SectionHeaders || SectionContents || SymbolTable ||
      DynamicSymbolTable || UnwindInfo || FaultMapSection || Offloading ||
      (MachOOpt &&
       (Bind || DataInCode || ChainedFixups || DyldInfo || DylibId ||
        DylibsUsed || ExportsTrie || FirstPrivateHeader ||
        FunctionStartsType != FunctionStartsMode::None || IndirectSymbols ||
        InfoPlist || LazyBind || LinkOptHints || ObjcMetaData || Rebase ||
        Rpaths || UniversalHeaders || WeakBind || !FilterSections.empty()));

  if (!ShouldDump && !PrintCpuHelp) {
    T->printHelp(ToolName);
    return 2;
  }

  // If the target triple is derived from the files, we display help message
  // when disassembling them.
  if (!Disassemble && PrintCpuHelp) {
    mcpuHelp();
    if (!ShouldDump)
      return EXIT_SUCCESS;
  }
```

Unfortunately, I wasn't able to come up with a cleaner implementation at this time.

Regarding the test cases, I assume that other error scenarios are already handled in other files.

Do you consider these cases sufficient for this PR? 

https://github.com/llvm/llvm-project/pull/165661