Fix Issue 23157 - undefined reference to `__cmsg_nxthdr' on Alpine Li…

[tom-tan]

…nux (musl libc)

The current definition of CMSG_NXTHDR uses __cmsg_nxthdr internally but __cmsg_nxthdr is not provided on Alpine Linux (musl libc). This request fixes the issue 23157 by fixing the definiiton of CMSG_NXTHDR.

Here is a corresponding definition in musl libc header: https://git.musl-libc.org/cgit/musl/tree/include/sys/socket.h#n357

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	23157	regression	undefined reference to `__cmsg_nxthdr' on Alpine Linux (musl libc)

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + druntime#3830"

[dkorpel]

Can you please rebase this to restart the CI?

[ljmf00]

Buildkite succeeded now, but FreeBSD still has heisenbugs. Seems unrelated.