Store latest redeclaration for each redeclarable template declaration

This patch adds a Latest field to RedeclarableTemplateDecl's CommonBase
class which is used to store the latest redeclaration.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@109755 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/PCHWriterDecl.cpp b/lib/Frontend/PCHWriterDecl.cpp
index 3ac4958..75045eb 100644
--- a/lib/Frontend/PCHWriterDecl.cpp
+++ b/lib/Frontend/PCHWriterDecl.cpp
@@ -852,6 +852,8 @@
     Writer.AddDeclRef(D->getInstantiatedFromMemberTemplate(), Record);
     if (D->getInstantiatedFromMemberTemplate())
       Record.push_back(D->isMemberSpecialization());
+
+    Writer.AddDeclRef(D->getCommonPtr()->Latest, Record);
   }
 }