ignore or warn on setrlimit(RLIMIT_AS)

Originally reported on Google Code with ID 166

```
asan should do something with setrlimit(RLIMIT_AS):

Choices:
1. silently ignore and return 0 (success)
2. silently ignore and return -1 (failure). What should be errno then?
3. print a warning and return -1
4. print a warning and die
5. ???

Thoughts?

We need this in sanitizer_common for tsan and msan
```

Reported by `konstantin.s.serebryany` on 2013-03-12 14:11:21