[PATCH] SanitizerArgs: add ability to filter/diagnose unsupported sanitizers.

[Richard Smith]

  Yes, moving ownership of the `SanitizerArgs` from `Driver` to `ToolChain` makes sense to me; the latter is parameterized by a set of command-line arguments, the former is not. I also support this change =)

http://llvm-reviews.chandlerc.com/D1990