Added sock_recv_msg, sock_send_msg

[sadhbh-c0d3]

Summary

Adds WASIX WITX ABI definitions for sock_send_msg and sock_recv_msg.

These syscalls model the WASIX side of POSIX sendmsg() / recvmsg() using:

• existing scatter/gather data iovecs,
• an optional socket address pointer,
• a raw control-message pointer and byte length,
• explicit returned data/control lengths.

This also adds the minimal WASIX control-message ABI shape needed for future ancillary data support:

• sock_cmsg
• sock_cmsg_level
• sock_cmsg_type
• SOCKET control-message level
• RIGHTS control-message type, corresponding to POSIX SCM_RIGHTS

Motivation

libuv and Node-style runtimes use sendmsg() / recvmsg() for IPC paths, especially socketpair-based communication and file-descriptor passing. WASIX did not have ABI-level operations that could represent these calls, which forced libc/runtime layers either to avoid the POSIX path or to use incomplete workarounds.

This WITX change gives wasix-libc a proper ABI target for POSIX-compatible sendmsg() / recvmsg() wrappers, and gives Wasmer a runtime syscall surface where payload transfer works now and ancillary/control-message handling can be implemented cleanly next.

Related implementation work lives in the matching wasix-libc and Wasmer PRs.