tsan: add memory_limit_mb flag

The flag allows to bound maximum process memory consumption (best effort).
If RSS reaches memory_limit_mb, tsan flushes all shadow memory.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@191913 91177308-0d34-0410-b5e6-96231b3b80d8