In 5.3, if an Objective-C method declared in a header shares the same name as an inaccessible Swift method, then the compiler considers the method to be inaccessible. As a workaround, rename the Swift method and stop emitting a symbol for it.
This is not a problem on the trunk, but there is no reason to expose this symbol there, either.
Move the ObjC class name stability check logic to the Swift runtime, exposing it as a new SPI called _swift_isObjCTypeNameSerializable.
Update the reporting logic. The ObjC names of generic classes are considered stable now, but private classes and classes defined in function bodies or other anonymous contexts are unstable by design.
On the overlay side, rewrite the check’s implementation in Swift and considerably simplify it.
rdar://57809977
