Part of adding an improved ODR checker.

Reserve a spot for ODR hash in CXXRecordDecl and in its modules storage.
Default the hash value to 0 for all classes.

Differential Revision: https://reviews.llvm.org/D21675

llvm-svn: 295533
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 5dee86c..5fe693b 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5707,6 +5707,7 @@
   Record->push_back(Data.ImplicitCopyAssignmentHasConstParam);
   Record->push_back(Data.HasDeclaredCopyConstructorWithConstParam);
   Record->push_back(Data.HasDeclaredCopyAssignmentWithConstParam);
+  Record->push_back(Data.ODRHash);
   // IsLambda bit is already saved.
 
   Record->push_back(Data.NumBases);