If various checks are omitted, the CMSG_NXTHDR macro expands to
(struct cmsghdr *)((char *)(cmsg) + \
_ALIGN(((struct cmsghdr *)(cmsg))->cmsg_len))
Although there is no alignment problem (assuming cmsg is properly aligned
and _ALIGN is correct), this violates -Wcast-align on strict-alignment
architectures. Therefore an intermediate cast to void * is appropriate here.
There is no workaround other than not using -Wcast-align.
MFC after: 2 weeks
a4646b9313