Ticket #3665: fix compatibility with netbsd curses.

The code that manipulates the ncurses backend into changing
the key combination to generate SIGINT from CTRL-c to CTRL-g does
so by accessing undocumented internal ncurses data structures.
This breaks compilation with netbsd-curses[0], and could also break
when the ncurses author decides to change internal structures in a
future release.

Fix it by using a portable approach that works everywhere using libc
primitives instead.

[0] https://github.com/sabotage-linux/netbsd-curses

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

lib/tty/tty-ncurses.c

@@ -179,6 +179,7 @@ mc_tty_normalize_lines_char (const char *ch)
 void
 tty_init (gboolean mouse_enable, gboolean is_xterm)
 {
+    struct termios mode;
     initscr ();
 
 #ifdef HAVE_ESCDELAY
@@ -194,11 +195,12 @@ tty_init (gboolean mouse_enable, gboolean is_xterm)
     ESCDELAY = 200;
 #endif /* HAVE_ESCDELAY */
 
+    tcgetattr (STDIN_FILENO, &mode);
     /* use Ctrl-g to generate SIGINT */
-    cur_term->Nttyb.c_cc[VINTR] = CTRL ('g');   /* ^g */
+    mode.c_cc[VINTR] = CTRL ('g');      /* ^g */
     /* disable SIGQUIT to allow use Ctrl-\ key */
-    cur_term->Nttyb.c_cc[VQUIT] = NULL_VALUE;
-    tcsetattr (cur_term->Filedes, TCSANOW, &cur_term->Nttyb);
+    mode.c_cc[VQUIT] = NULL_VALUE;
+    tcsetattr (STDIN_FILENO, TCSANOW, &mode);
 
     tty_start_interrupt_key ();