Repoison the entire ASan chunk if it is not in active use.

Summary:
Repoisoning just the minimal redzones might leave an unpoisoned
gap of the size of the actual redzone minus minimal redzone size.
After ASan activation the actual redzone might be bigger than the minimal
size and ASan allocator assumes that the chunk returned by the common
allocator is either entirely poisoned or entirely not poisoned (it's too
expensive to check the entire chunk or always poison one).

Reviewers: eugenis

Subscribers: kubabrecka, llvm-commits

Differential Revision: https://reviews.llvm.org/D28577

llvm-svn: 291714