Fix DIBuilder::createVariantPart after f6617d65e496
which ended up passing 0 for the Discriminator arg, Discriminator for
the DataLocation arg, etc.
The DICompositeType::get's new NumExtraInhabitants parameter is at the
end, and has a default value, so no change in the caller is necessary.
See comment on https://github.com/llvm/llvm-project/pull/112590
