This removes the -use-native-super-method flag and turns on dynamic
dispatch for native method invocations on super by default.
rdar://problem/22749732
Use the `super_method` instruction for non-final `func` and `class func`
declarations in native Swift classes. Previously, we would always emit
a static `function_ref` for these, which prevents resilient dynamic
dispatch.
This is hidden behind a -use-native-super-dispatch flag while I
survey the effects on devirtualization and stack promotion. When
that's figured out, I'll add more tests and update test cases that
still assume static dispatch.
rdar://problem/22749732
