[sanitizer] Handle Die() in StopTheWorld.

Handle calls to Die() from the tracer thread. Fixes a bug where a CHECK
could fail in the tracer thread, resulting in a call to AsanDie. The tracer
thread then exited and the parent process continued execution despite its
address space being in an unusable state.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@189216 91177308-0d34-0410-b5e6-96231b3b80d8