Stefan Krah: "we care about the C11 restriction? (...) "size - number of bytes to allocate. An integral multiple of alignment" (...) posix_memalign and _aligned_malloc don't care about the multiple."

I prefer to ignore this restriction at this point.

I wouldn't be surprised if posix_memalign() and _aligned_malloc() already align the size for us internally.

We can add the restriction later, if needed.