swift234

[SourceKit] For clang enums imported as error domains, make sure to use unique USRs.

Error domain enums are imported with synthesizing something like this:

 struct MyError {
     enum Code : Int32 {
         case errFirst
         case errSecond
     }
     static var errFirst: MyError.Code { get }
     static var errSecond: MyError.Code { get }
 }

The clang enum and enum constants are associated with both the
struct/nested enum, and the static vars/enum cases.
But we want unique USRs for the above symbols, so use the clang USR
for the enum and enum cases, and the Swift USR for the struct and vars.

rdar://27550967