Add a "fork" of musl as //fusl.

fusl/src/network/sendmsg.c

+#include <sys/socket.h>
+#include <limits.h>
+#include <string.h>
+#include <errno.h>
+#include "syscall.h"
+#include "libc.h"
+
+ssize_t sendmsg(int fd, const struct msghdr *msg, int flags)
+{
+#if LONG_MAX > INT_MAX
+        struct msghdr h;
+        struct cmsghdr chbuf[1024/sizeof(struct cmsghdr)+1], *c;
+        if (msg) {
+                h = *msg;
+                h.__pad1 = h.__pad2 = 0;
+                msg = &h;
+                if (h.msg_controllen) {
+                        if (h.msg_controllen > 1024) {
+                                errno = ENOMEM;
+                                return -1;
+                        }
+                        memcpy(chbuf, h.msg_control, h.msg_controllen);
+                        h.msg_control = chbuf;
+                        for (c=CMSG_FIRSTHDR(&h); c; c=CMSG_NXTHDR(&h,c))
+                                c->__pad1 = 0;
+                }
+        }
+#endif
+        return socketcall_cp(sendmsg, fd, msg, flags, 0, 0, 0);
+}