Refactoring llvm command line parsing and option registration.

Summary:
The primary goal of this patch is to remove the need for MarkOptionsChanged(). That goal is accomplished by having addOption and removeOption properly sort the options.

This patch puts the new add and remove functionality on a CommandLineParser class that is a placeholder. Some of the functionality in this class will need to be merged into the OptionRegistry, and other bits can hopefully be in a better abstraction.

This patch also removes the RegisteredOptionList global, and the need for cl::Option objects to be linked list nodes.

The changes in CommandLineTest.cpp are required because these changes shift when we validate that options are not duplicated. Before this change duplicate options were only found during certain cl API calls (like cl::ParseCommandLine). With this change duplicate options are found during option construction.

Reviewers: dexonsmith, chandlerc, pete

Reviewed By: pete

Subscribers: pete, majnemer, llvm-commits

Differential Revision: http://reviews.llvm.org/D7132

llvm-svn: 227345