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

[Manuel Klimek]

  LG. Note that this change is an exception to the usually very strong principle I have to never check in code that is not needed right away. The main reason to me for allowing it in is that it merely exposes the interface of cl::ParseCommandLineOptions, and that there are external users of this interface that I cannot ask whether they want the change right away.

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

BRANCH
  tool-cli-overview

ARCANIST PROJECT
  clang