[TSanRuntime] Upstream thread swift race detector.

Summary:
This is self-contained, and doesn't need anything in the
compiler to work. Mainly to reduce the diff between upstream
and downstream.

Patch by Kuba Mracek!

Reviewers: kubamracek

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D66915

llvm-svn: 370286