tsan: deannotating benign data races

Originally reported on Google Code with ID 41

```
ThreadSanitizer allows to specify that data races inside a particular
memory region are benign. However, it is impossible to remove a region
from the list of those with benign data races. Once the region is
reallocated and used for a different purpose, real data races on it may
be missed.

I propose adding such a "deannotation" functionality to ThreadSanitizer.
A possible patch:

https://github.com/yegord/compiler-rt/commit/DeannotateBenignRace

```

Reported by `yegor.derevenets` on 2013-11-20 14:52:22