[clang] [lld] [lldb] [llvm] [Option] Replace the OptionTables object with a function. NFC (PR #224805)

[Alexis Engelke via cfe-commits]

https://github.com/aengelke commented:

> Derive the prefix union from the prefix table in the constructor and drop the emitted OptionPrefixesUnion.

What's the motivation here? This doesn't look strictly required to be in the same patch, and I'd prefer that to be separate.

https://github.com/llvm/llvm-project/pull/224805