Erroneous declaration attributes were sometimes being printed in the private swiftinterfaces of modules because the changes from https://github.com/apple/swift/pull/42276 were effectively corrupting the attribute list for any decl with sythesized conformances (e.g. `Equatable`, `Hashable`). It is necessary to clone the attributes before adding them to the synthesized conformance extension decls.
Resolves rdar://94009296
