Prior to this patch, SwiftLookupTable::translateDeclToContext relied
on the `TypedefNameDeclOrQualifier` field of an anonymous tag decl to
create a name for entry representing an anonymous tag in the lookup
table. This field is not always populated by Clang, it is often
populated only for the purposes of generating a linkage name when the
type is introduced via typedef as follows:
```
typedef enum { option1, option2} MyAnonEnum;
```
The field is not populated for anonymous enums introduced by NS_OPTIONS
with cxx interop enabled. This patch adds a fallback check in
`translateDeclToContext` that if the field is empty, check if the enum
is backed by a typedef that is unavailable in Swift. If that is the
case, use that name for the lookup table entry.
