[PATCH] [sanitizer] Fix log_path behavior with StopTheWorld.

[Alexey Samsonov]

  IMO it's not an excuse to add that much complexity. The code is bad already, and this change makes these subtle modifications of global state worse. If we decide to use a single file for parent and tracer task, we may just pass a "log_pid" parameter into MaybeOpenReportFile() function, that would generally be just "internal_getpid()", but be the pid of parent process inside tracer task.

http://llvm-reviews.chandlerc.com/D2306