utils: Add wrappers for memcpy(3), memmove(3) and memset(3)

utils: Add wrappers for memcpy(3), memmove(3) and memset(3)

These wrappers guarantee that calls to these functions are noops if the
number of bytes is 0, as calling them with NULL pointers is undefined
according to the C standard, even if the number of bytes is 0 (most
implementations probably ignore the pointers anyway in this case, but
lets make sure).