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

[Dmitri Gribenko]

  Oh, and one more thing.  Please add two tests:

  1) a driver test to check that options are forwarded to cc1 properly.  For example, take a look at ../../test/Driver/retain-comments-from-system-headers.c

  2) add a test that is like the testcases in test/Index/comment-to-html-xml-conversion.cpp, but uses custom commands.  This is to check that -cc1 option really works.

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