[ASan] Implement asan_mz_size(), asan_mz_force_lock() and asan_mz_force_unlock() for allocator2.
Switch to allocator2 on Darwin.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@174603 91177308-0d34-0410-b5e6-96231b3b80d8