[PATCH] [sanitizer] Support adaptive stack unwinding in sanitizer tools.

[Sergey Matveev]

  There are still two things I don't like about this:
  1. It could degenerate into just using the slow unwinder all the time, and the tests would never notice. (benchmarks?)
  2. The threaded test doesn't really test the actual code, because we can't use the real sanitizer_thread_start functions. I wonder if we should factor out the boilerplate stuff from those functions (name, calling convention, the asm blob at the end) into a macro in sanitizer_common?

http://llvm-reviews.chandlerc.com/D1378