Add an option to parse all comments as documentation comments

Patch by Amin Shali.

llvm-svn: 179180
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index cf93d1c..03e33ad 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1069,6 +1069,7 @@
        I != IEnd; ++I) {
     AddString(*I, Record);
   }
+  Record.push_back(LangOpts.CommentOpts.ParseAllComments);
 
   Stream.EmitRecord(LANGUAGE_OPTIONS, Record);