Move SanitizerArgs to the clang Driver

Summary:
This change turns SanitizerArgs into high-level options
stored in the Driver, which are parsed lazily. This fixes an issue of multiple copies of the same diagnostic message produced by sanitizer arguments parser.

Reviewers: rsmith

Reviewed By: rsmith

CC: chandlerc, eugenis, cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1341