Memory Alignment issues on ARM processors

Unaligned data on ARM architectures do not perform efficiently unaligned
memory access, and in the case of ARMv7 and iOS it completely breaks. The OCB
algorithm dereferences a uint64x2_t pointer, and is replaced by a
memcpy to avoid penalties when trying to align it.

More info https://brewx.qualcomm.com/bws/content/gi/common/appseng/en/knowledgebase/docs/kb95.html