[PATCH] Option parsing: support case-insensitive option matching.

[Rui Ueyama]

  I noticed that this patch changes the order of options shown by "--help". Before this patch the options
  are sorted in asciibetical order, but with this patch they are sorted in a case insensitive manner.

  So I took a look at other tools to see if it's a bad thing. GNU tools seems to list options in a case insensitive
  manner if --help is given; I tested with sort, od and ls (gcc shows options in some random order though). So
  are true for non-GNU commands, such as Python or Ruby. Thus, I don't think changing the sort order is going
  to be a problem, but correct me if there's a concern.

http://llvm-reviews.chandlerc.com/D1485