1. Change some "\n" -> '\n'.
2. eliminte some std::string's by using raw_ostream::indent.
3. move a bunch of code out of the main arg parser routine into
   a new static HandlePrefixedOrGroupedOption function.
4. Greatly simplify the implementation of getOptionPred, and make
   it avoid splitting prefix options at = when that doesn't match
   a non-prefix option.

llvm-svn: 82362