swift234

[serialization] Always serialize conformance data for imported decls.

Some AST nodes and SIL instructions need to reference conformances for a
particular type. If that type was imported from Clang, however, the
conformance may not exist when the AST node or SIL function gets deserialized
later. The SIL case is the problem case: fragile SIL code may contain a
reference to a conformance never mentioned in the AST of the code being
compiled, and since conformances are synthesized on demand during type-checking,
this will lead to a crash. SIL deserialization isn't supposed to be doing
work on its own (though it ~can~ import new Clang decls at the moment), so
the best answer is to serialize the conformances directly, like we would with
specialized or inherited conformances.

We can probably do better here in the long run (we don't even unique
conformances like this within a module), but this should at least handle the
immediately known problem cases.

rdar://problem/18669402

Swift SVN r22857