[lsan] Make LSan ignore memory poisoned by ASan.

Summary:
No more (potenital) false negatives due to red zones or fake stack
frames.

Reviewers: kcc, samsonov

Reviewed By: samsonov

CC: llvm-commits, samsonov

Differential Revision: http://llvm-reviews.chandlerc.com/D2359

llvm-svn: 196778