This is a new attempt of https://reviews.llvm.org/D159481, this time as
GitHub PR.
`GenericOptionValue::compare()` should return `true` for a match.
- `OptionValueBase::compare()` always returns `false` and shouldn't
match anything.
- `OptionValueCopy::compare()` returns `false` if not `Valid` which
corresponds to no match.
Also adding some tests.
710b5a1232