[tsan] Enable tsan's deadlock detector by default.

The tsan's deadlock detector has been used in Chromium for a while;
it found a few real bugs and reported no false positives.
So, it's time to give it a bit more exposure.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@212533 91177308-0d34-0410-b5e6-96231b3b80d8