Sema: Keep track of per-source file synthesized declarations

This allows conformance checking to be performed after all
members of a type have been type checked.

include/swift/AST/Module.h

@@ -854,6 +854,14 @@ public:
   /// complete, we diagnose.
   llvm::SetVector<const DeclAttribute *> AttrsRequiringFoundation;
 
+  /// A set of synthesized declarations that need to be type checked.
+  llvm::SmallVector<Decl *, 8> SynthesizedDecls;
+
+  /// We might perform type checking on the same source file more than once,
+  /// if its the main file or a REPL instance, so keep track of the last
+  /// checked synthesized declaration to avoid duplicating work.
+  unsigned LastCheckedSynthesizedDecl = 0;
+
   /// A mapping from Objective-C selectors to the methods that have
   /// those selectors.
   llvm::DenseMap<ObjCSelector, llvm::TinyPtrVector<AbstractFunctionDecl *>>