drivers/serial: Integrate new Ctrl-C logic with the ISIG flag in the termios c_lflag. Fix several compiler errors resulting from recently flurry of renaming.

include/nuttx/serial/serial.h

@@ -286,10 +286,9 @@ struct uart_dev_s
   tcflag_t             tc_iflag;     /* Input modes */
   tcflag_t             tc_oflag;     /* Output modes */
   tcflag_t             tc_lflag;     /* Local modes */
+#ifdef CONFIG_TTY_SIGKILL
+  pid_t                pid;          /* Thread PID to receive SIGKILL signals (-1 if none) */
 #endif
-
-#ifdef CONFIG_SERIAL_SIGKILL_CHAR
-  pid_t                 pid;         /* Thread PID to receive SIGKILL signals (-1 if none) */
 #endif
 
   /* Semaphores */