Reimplement circularly check for protocol inheritance.

First, make it actually check for cycles properly. Second, pull it
into the checking of the protocol itself, rather than keeping it as a
separate pass that happens too late to be useful. Finally, put the
unchecked/checking/checked bits into the AST to avoid having to keep a
separate DenseMap just for this purpose. Fixes <rdar://problem/14750346>.


Swift SVN r7324

lib/Serialization/ModuleFile.cpp

@@ -1036,6 +1036,7 @@ Decl *ModuleFile::getDecl(DeclID DID, Optional<DeclContext *> ForcedContext,
     assert(members.hasValue() && "could not read struct members");
     proto->setMembers(members.getValue(), SourceRange());
     proto->setCheckedInheritanceClause();
+    proto->setCircularityCheck(CircularityCheck::Checked);
     break;
   }