[PATCH] Add CommentOptions, allow specifying custom comment block commands

[Dmitri Gribenko]

  Right.  This is the PCH test failing.  You need to serialize/deserialize CommentOptions into/from PCH.  Please look at ASTWriter::WriteControlBlock, it serializes LangOptions, you should write CommentOptions there.  And there is a symmetrical ASTReader::ParseLanguageOptions for reading.

http://llvm-reviews.chandlerc.com/D272