Rework the traversal of Objective-C categories and extensions to
consider (sub)module visibility.

The bulk of this change replaces myriad hand-rolled loops over the
linked list of Objective-C categories/extensions attached to an
interface declaration with loops using one of the four new category
iterator kinds:

  visible_categories_iterator: Iterates over all visible categories
  and extensions, hiding any that have their "hidden" bit set. This is
  by far the most commonly used iterator.

  known_categories_iterator: Iterates over all categories and
  extensions, ignoring the "hidden" bit. This tends to be used for
  redeclaration-like traversals.

  visible_extensions_iterator: Iterates over all visible extensions,
  hiding any that have their "hidden" bit set.

  known_extensions_iterator: Iterates over all extensions, whether
  they are visible to normal name lookup or not.

The effect of this change is that any uses of the visible_ iterators
will respect module-import visibility. See the new tests for examples.

Note that the old accessors for categories and extensions are gone;
there are *Raw() forms for some of them, for those (few) areas of the
compiler that have to manipulate the linked list of categories
directly. This is generally discouraged.

Part two of <rdar://problem/10634711>.
 

llvm-svn: 172665
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index bc92fb7..7a57bad 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -491,13 +491,14 @@
            PEnd = Data.AllReferencedProtocols.end();
          P != PEnd; ++P)
       Writer.AddDeclRef(*P, Record);
+
     
-    if (ObjCCategoryDecl *Cat = D->getCategoryList()) {
+    if (ObjCCategoryDecl *Cat = D->getCategoryListRaw()) {
       // Ensure that we write out the set of categories for this class.
       Writer.ObjCClassesWithCategories.insert(D);
       
       // Make sure that the categories get serialized.
-      for (; Cat; Cat = Cat->getNextClassCategory())
+      for (; Cat; Cat = Cat->getNextClassCategoryRaw())
         (void)Writer.GetDeclRef(Cat);
     }
   }