Provide standards-based aligned_alloc() function in VecCore
The recent fix in commit d9f96b12 was ignoring the return value of posix_memalign(), which led to compiler warnings on Linux. This commit implements the aligned_alloc() function from C11 standard using posix_memalign() on Apple systems.
Reference: http://en.cppreference.com/w/c/memory/aligned_alloc