Improved support for language types as command

options:

- added help ("help language") listing the
  possible options;

- added the possibility of synonyms for language
  names, in this case "ObjC" for "Objective-C";
  and

- made matching against language names case
  insensitive.

This should improve discoverability.

<rdar://problem/12552359>

llvm-svn: 166457