[PATCH] Moar string interceptors: strstr, strcasestr, strcspn, strpbrk

[Yury Gribov]

> Because the standards are unlikely to define which optimizations are applicable to each function,
> I think we'd better be more conservative here.

That's questionable. Some users (e.g. me) would very much prefer to get a warning even about potential errors. Can we have a flag for this like we already have for strict_memcmp and alloc_dealloc_mismatch?

http://reviews.llvm.org/D6056