[clang] [clang-tools-extra] [lld] [llvm] [llvm] Add subcommand support for OptTable (PR #155026)

[via llvm-commits]

================
@@ -169,6 +198,10 @@ class LLVM_ABI OptTable {
   OptTable(const StringTable &StrTable,
            ArrayRef<StringTable::Offset> PrefixesTable,
            ArrayRef<Info> OptionInfos, bool IgnoreCase = false);
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PiJoules wrote:

Could probably just add 

```
ArrayRef<Command> Commands = {},
ArrayRef<unsigned> CommandIDsTable = {},
```

so you don't need to make another ctor. Same with other OpTables below.

https://github.com/llvm/llvm-project/pull/155026