Adopt new cl::HideUnrelatedOptions API added r226729.

Summary: cl::HideUnrelatedOptions allows tools to hide all options not part of a specific OptionCategory. This is the common use case for cl::getRegisteredOptions, which should be deprecated in the future because it exposes implementation details of command line parsing.

Reviewers: dexonsmith

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D7109

llvm-svn: 226741