system/cu: make the cu tool can work with SIGNAL disabled

Use CONFIG_DISABLE_SIGNALS to conditionally compile signal handling
code, allowing cu to work on systems with signals disabled.

Signed-off-by: guoshichao <guoshichao@xiaomi.com>

Author: extinguish

system/cu/cu_main.c

@@ -153,7 +153,7 @@ static FAR void *cu_listener(FAR void *parameter)
   return NULL;
 }
 
-#ifdef CONFIG_ENABLE_ALL_SIGNALS
+#ifndef CONFIG_DISABLE_SIGNALS
 static void cu_exit(int signo, FAR siginfo_t *siginfo, FAR void *context)
 {
   FAR struct cu_globals_s *cu = siginfo->si_user;
@@ -307,7 +307,7 @@ static int cu_cmd(FAR struct cu_globals_s *cu, char bcmd)
 int main(int argc, FAR char *argv[])
 {
   pthread_attr_t attr;
-#ifdef CONFIG_ENABLE_ALL_SIGNALS
+#ifndef CONFIG_DISABLE_SIGNALS
   struct sigaction sa;
 #endif
   struct cu_globals_s cu;
@@ -329,7 +329,8 @@ int main(int argc, FAR char *argv[])
 
   memset(&cu, 0, sizeof(cu));
   cu.escape = '~';
-#ifdef CONFIG_ENABLE_ALL_SIGNALS
+
+#ifndef CONFIG_DISABLE_SIGNALS
   /* Install signal handlers */
 
   memset(&sa, 0, sizeof(sa));
@@ -343,6 +344,7 @@ int main(int argc, FAR char *argv[])
       return EXIT_FAILURE;
     }
 #endif
+
   optind = 0;   /* Global that needs to be reset in FLAT mode */
   while ((option = getopt(argc, argv, "l:s:ceE:fho?")) != ERROR)
     {