[PATCH] gdb: fix build with gcc-15 and -std=c23

[Rudi Heitbaum <rudi@heitbaum.com>]

int signum is required to be passed to SigHandler.
readline-8.2 has updated this typedef in the upstream 8.2

fixes:
    ../../../readline/readline/signals.c: In function 'rl_set_signals':
    ../../../readline/readline/signals.c:480:40: error: passing argument 2 of 'rl_maybe_set_sighandler' from incompatible pointer type [-Wincompatible-pointer-types]
      480 |       rl_maybe_set_sighandler (SIGINT, rl_signal_handler, &old_int);
          |                                        ^~~~~~~~~~~~~~~~~
          |                                        |
          |                                        void (*)(int)
    ../../../readline/readline/signals.c:407:47: note: expected 'void (*)(void)' but argument is of type 'void (*)(int)'
      407 | rl_maybe_set_sighandler (int sig, SigHandler *handler, sighandler_cxt *ohandler)
          |                                   ~~~~~~~~~~~~^~~~~~~

Signed-off-by: Rudi Heitbaum <rudi@heitbaum.com>
---
 readline/readline/signals.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/readline/readline/signals.c b/readline/readline/signals.c
index 8fedc370a1a..28f5366030c 100644
--- a/readline/readline/signals.c
+++ b/readline/readline/signals.c
@@ -64,7 +64,7 @@
 
 /* This typedef is equivalent to the one for Function; it allows us
    to say SigHandler *foo = signal (SIGKILL, SIG_IGN); */
-typedef RETSIGTYPE SigHandler ();
+typedef RETSIGTYPE SigHandler (int);
 
 #if defined (HAVE_POSIX_SIGNALS)
 typedef struct sigaction sighandler_cxt;
-- 
2.43.0