swift234

[Accessibility] Store setter accessibility explicitly.

Previously, we were just storing setter accessibility via the accessibility
level on the setter function. However, some Stored properties never actually
have a setter synthesized, which led to the compiler dropping the setter
accessibility at serialization time. Rather than try to hack up something
clever, just store the setter accessibility explicitly in every
AbstractStorageDecl. (We still only serialize it for VarDecls, because
settable SubscriptDecls always have setter functions.)

<rdar://problem/17816530>

Swift SVN r20598