Parser/Registry argument enhancements.

Summary:
 Parser/Registry argument enhancements.
  - 2 argument support.
  - unsigned values support.

Reviewers: klimek

CC: cfe-commits, revane

Differential Revision: http://llvm-reviews.chandlerc.com/D915

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183231 91177308-0d34-0410-b5e6-96231b3b80d8