In general, this forces SILGen and IRGen code that's grabbing
a declaration to state whether it's doing so to define it.
Change SIL serialization to serialize the linkage of functions
and global variables, which means also serializing declarations.
Change the deserializer to use this stored linkage, even when
only deserializing a declaration, and to call a callback to
inform the client that it has deserialized a new entity.
Take advantage of that callback in the linking pass to alter
the deserialized linkage as appropriate for the fact that we
imported the declaration. This computation should really take
advantage of the relationship between modules, but currently
it does not.
Swift SVN r12090
This will let us control linkage and emit new variables independent of the AST in SILGen. In particular, for lazy global initialization, we need to emit a unique internal once predicate for every top-level pattern binding. Switching everything over is a bit much to reengineer all at once, so for now, it can coexist with the globals map that is already there.
Swift SVN r10509
