[asan] Fix a deadlock between asan's allocator and lsan

Summary:
This fixes a deadlock which happens in lsan
on a large memalign-allocated chunk that resides in lsan's root set.

Reviewers: samsonov, earthdok

Reviewed By: earthdok

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1957