[PATCH] Allow Clang tools to display an overview when using the CommonOptionsParser.

[Manuel Klimek]

  See http://clang.llvm.org/doxygen/classclang_1_1tooling_1_1CommonOptionsParser.html
  Isn't that already possible with:
   static cl::extrahelp CommonHelp(CommonOptionsParser::HelpMessage);
   static cl::extrahelp MoreHelp("\nMore help text...");
   static cl:opt<bool> YourOwnOption(...);

http://llvm-reviews.chandlerc.com/D1185