[RFC] Multilib

Does this mean that you can do the following?

Variants:
  - Dir: itanium
    Tags: [fc++abi=itanium]
    PrintOptions: [-fc++abi=itanium]

If that’s the case then I think the original name “flags” is a better fit than “tags”. I apologize about going back on forth on this. It might be also worth including this example in the documentation.