If we manually poison memory region, ASAN requires that we manually unpoison
it too. We didn't do it and munmap() didn't do it too. That was the issue.

os_mem_free_large(): unpoison memory region. Just in case.

https://github.com/google/sanitizers/issues/182
https://github.com/llvm/llvm-project/blob/86acaa9457d3957cbe303e1e801f1e727f66ca89/compiler-rt/include/sanitizer/asan_interface.h#L21