readline() is careful not to read more bytes from fd 0 than it has to.
Do the same in the dummy libss readline() by disabling stdin
buffering.
ticket: 8745
struct termios termbuf;
char input[BUFSIZ];
+ /* Make sure we don't buffer anything beyond the line read. */
+ setvbuf(stdin, 0, _IONBF, 0);
+
if (tcgetattr(STDIN_FILENO, &termbuf) == 0) {
termbuf.c_lflag |= ICANON|ISIG|ECHO;
tcsetattr(STDIN_FILENO, TCSANOW, &termbuf);