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

fusl/src/network/socketpair.c

+#include <sys/socket.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "syscall.h"
+
+int socketpair(int domain, int type, int protocol, int fd[2])
+{
+        int r = socketcall(socketpair, domain, type, protocol, fd, 0, 0);
+        if (r<0 && (errno==EINVAL || errno==EPROTONOSUPPORT)
+            && (type&(SOCK_CLOEXEC|SOCK_NONBLOCK))) {
+                r = socketcall(socketpair, domain,
+                        type & ~(SOCK_CLOEXEC|SOCK_NONBLOCK),
+                        protocol, fd, 0, 0);
+                if (r < 0) return r;
+                if (type & SOCK_CLOEXEC) {
+                        __syscall(SYS_fcntl, fd[0], F_SETFD, FD_CLOEXEC);
+                        __syscall(SYS_fcntl, fd[1], F_SETFD, FD_CLOEXEC);
+                }
+                if (type & SOCK_NONBLOCK) {
+                        __syscall(SYS_fcntl, fd[0], F_SETFL, O_NONBLOCK);
+                        __syscall(SYS_fcntl, fd[1], F_SETFL, O_NONBLOCK);
+                }
+        }
+        return r;
+}