The execution of these functions is controlled by the testing
framework and it's okay if their behavior changes when the feature
flag is enabled.
Resolves: rdar://152687527
Prevent migration from handling declarations that come from a
module different from the current one, this is primarily a
problem for swiftinterfaces that can get rebuilt when the module
is imported by a model that has migration mode enabled.
Resolves: rdar://152687353
See the inline comments for more details. Depending on the closure's
type signature, sometimes adding the attribute will break code. Fix this
by also adding inferred effects to the signature in these cases.
