From termios(3): "XCASE (not in POSIX; not supported under Linux)".
musl does not define it, and even if defined it's a no-op.

Signed-off-by: Alex Suykov <alex.suykov@gmail.com>

--- a/posix.c
+++ b/posix.c
@@ -65,7 +65,7 @@
 	    ~(OPOST | ONLCR | OLCUC | OCRNL | ONOCR | ONLRET);
 
 	/* No signal handling, no echo etc */
-	ntermios.c_lflag &= ~(ISIG | ICANON | XCASE | ECHO | ECHOE | ECHOK
+	ntermios.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK
 			      | ECHONL | NOFLSH | TOSTOP | ECHOCTL |
 			      ECHOPRT | ECHOKE | FLUSHO | PENDIN | IEXTEN);