The current ABI of dynamic is not what we want for certain declarations.
e.g
dynamic var x : Int {
willset {
}
}
Is exposed in the .swiftinterface file as
dynamic var x : Int {
get {}
set {}
}
However, the actual implementation is marking the willSet only dynamic.
var x : Int {
dynamic willSet() {}
get {}
set {}
}
To be able to rely on `dynamic` in the future we disable dynamic (for
non-@objc) under library-evolution for now until we have made sure that
the ABI is proper.
rdar://51678074
