[Sanitizers] Add more standard compliant posix_memalign implementation for LSan.

Summary:
Add more standard compliant posix_memalign implementation for LSan and
use corresponding sanitizer's posix_memalign implenetations in allocation
wrappers on Mac.

Reviewers: eugenis, fjricci

Subscribers: kubamracek, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D44335

llvm-svn: 327338