* Ignore -wmo when passing -dump-ast
* Cleanup on driver diagnostics
* Remove the FIXME.
* Add support for ignoring `-index-file`
* Revert unrelated formatting changes
* Revert back to only ignoring `-wmo`
Ignoring both `-wmo` and `-index-file` will be harder than just `-wmo`. This is because when calling the compiler and passing `-index-file` after `-dump-ast`, the option gets un-ignored by `Driver::buildOutputInfo`. Therefore, we will just ignore `-wmo` for now.
* Add tests, inspired by `Driver/batch_mode_with_WMO_or_index.swift`
