Change Parser & Sema to use interned "super" for comparions.

 - Added as private members for each because it is not clear where to
   put the common definition. Perhaps the IdentifierInfos all of these
   "pseudo-keywords" should be collected into one place (this would
   KnownFunctionIDs and Objective-C property IDs, for example).

Remove Token::isNamedIdentifier.
 - There isn't a good reason to use strcmp when we have interned
   strings, and there isn't a good reason to encourage clients to do
   so.

llvm-svn: 54794