kdb: move kdb_send_sig() declaration to a better header file

kdb_send_sig() is defined in the signal code and called from kdb,
but the declaration is part of the kdb internal code.
Move the declaration to the shared header to avoid the warning:

kernel/signal.c:4789:6: error: no previous prototype for 'kdb_send_sig' [-Werror=missing-prototypes]

Reported-by: Arnd Bergmann <arnd@arndb.de>
Closes: https://lore.kernel.org/lkml/20230517125423.930967-1-arnd@kernel.org/
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20230630201206.2396930-1-daniel.thompson@linaro.org

Author: Daniel Thompson

include/linux/kdb.h

@@ -196,6 +196,8 @@ int kdb_process_cpu(const struct task_struct *p)
 	return cpu;
 }
 
+extern void kdb_send_sig(struct task_struct *p, int sig);
+
 #ifdef CONFIG_KALLSYMS
 extern const char *kdb_walk_kallsyms(loff_t *pos);
 #else /* ! CONFIG_KALLSYMS */

kernel/debug/kdb/kdb_private.h

@@ -194,7 +194,6 @@ extern char kdb_task_state_char (const struct task_struct *);
 extern bool kdb_task_state(const struct task_struct *p, const char *mask);
 extern void kdb_ps_suppressed(void);
 extern void kdb_ps1(const struct task_struct *p);
-extern void kdb_send_sig(struct task_struct *p, int sig);
 extern char kdb_getchar(void);
 extern char *kdb_getstr(char *, size_t, const char *);
 extern void kdb_gdb_state_pass(char *buf);