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

[Rui Ueyama]

  OK, then we have two choices. Duplicate the function as we did or move it to Support. I think duplicate the function would make sense as it's now just 8-line function. WDYT?

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

BRANCH
  ignore-case

ARCANIST PROJECT
  llvm