Now that we use the C names of imported types in mangled names, it's
safe to resolve a compatibility alias when a type gets an
NS_SWIFT_NAME for the first time, rather than requiring the developer
to recompile the imported library.
This doesn't include generic types, which only applies for Objective-C
generics. There shouldn't be additional complications here but I want
to be extra careful.
rdar://problem/39661212
