The Clang attribute allows one to state that a particular enumeration
type describes an error, and associates it with a particular domain
constant. However, due to lack of API notes support, this attribute
wasn't actually getting used. Instead, we had a number of explicit
extensions to enum types to make them conform to the _BridgedNSError
protocol explicitly.
Now that we have API notes, use them to make these enums into error
enums with the appropriate domain, so that the Clang importer will
synthesize the _BridgedNSError conformances. Then, remove all of the
explicit conformances---and with them, the overlays for 12 frameworks.
There is a small fix to more eagerly consider these conformances as
"used" if an expression is formed with the error enum as a value
type. This better ensures that the conformances will be available at
runtime when needed.
This cleanup is needed to implement SE-0112 (NSError bridging),
although it is useful by itself.
In iOS 9 and OS X 10.11 the old GameKit was effectively renamed GameCenter, while
the new GameKit is a sort of umbrella framework like Cocoa. We need to support
backwards deployment, though, so the GameCenter overlay links to GameKit.framework.
(This is essentially the same solution implemented for CoreImage moving out of
QuartzCore in r28449)
rdar://problem/21340738
Swift SVN r30322
