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

fusl/src/unistd/pipe2.c

+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include "syscall.h"
+
+int pipe2(int fd[2], int flag)
+{
+        if (!flag) return pipe(fd);
+        int ret = __syscall(SYS_pipe2, fd, flag);
+        if (ret != -ENOSYS) return __syscall_ret(ret);
+        ret = pipe(fd);
+        if (ret) return ret;
+        if (flag & O_CLOEXEC) {
+                __syscall(SYS_fcntl, fd[0], F_SETFD, FD_CLOEXEC);
+                __syscall(SYS_fcntl, fd[1], F_SETFD, FD_CLOEXEC);
+        }
+        if (flag & O_NONBLOCK) {
+                __syscall(SYS_fcntl, fd[0], F_SETFL, O_NONBLOCK);
+                __syscall(SYS_fcntl, fd[1], F_SETFL, O_NONBLOCK);
+        }
+        return 0;
+}