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

fusl/src/misc/openpty.c

+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <pty.h>
+#include <stdio.h>
+#include <pthread.h>
+
+/* Nonstandard, but vastly superior to the standard functions */
+
+int openpty(int *pm, int *ps, char *name, const struct termios *tio, const struct winsize *ws)
+{
+        int m, s, n=0, cs;
+        char buf[20];
+
+        m = open("/dev/ptmx", O_RDWR|O_NOCTTY);
+        if (m < 0) return -1;
+
+        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+
+        if (ioctl(m, TIOCSPTLCK, &n) || ioctl (m, TIOCGPTN, &n))
+                goto fail;
+
+        if (!name) name = buf;
+        snprintf(name, sizeof buf, "/dev/pts/%d", n);
+        if ((s = open(name, O_RDWR|O_NOCTTY)) < 0)
+                goto fail;
+
+        if (tio) tcsetattr(s, TCSANOW, tio);
+        if (ws) ioctl(s, TIOCSWINSZ, ws);
+
+        *pm = m;
+        *ps = s;
+
+        pthread_setcancelstate(cs, 0);
+        return 0;
+fail:
+        close(m);
+        pthread_setcancelstate(cs, 0);
+        return -1;
+}