audit: avoid missing-prototype warnings

Building with 'make W=1' reveals two function definitions without
a previous prototype in the audit code:

lib/compat_audit.c:32:5: error: no previous prototype for 'audit_classify_compat_syscall' [-Werror=missing-prototypes]
kernel/audit.c:1813:14: error: no previous prototype for 'audit_serial' [-Werror=missing-prototypes]

The first one needs a declaration from linux/audit.h but cannot
include that header without causing conflicting (compat) syscall number
definitions, so move the it into linux/audit_arch.h.

The second one is declared conditionally based on CONFIG_AUDITSYSCALL
but needed as a local function even when that option is disabled, so
move the declaration out of the #ifdef block.

Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Paul Moore <[e-mail]>

include/linux/audit.h

···
 extern unsigned compat_chattr_class[];
 extern unsigned compat_signal_class[];
 
-extern int audit_classify_compat_syscall(int abi, unsigned syscall);
-
 /* audit_names->type values */
 #define	AUDIT_TYPE_UNKNOWN	0	/* we don't know yet */
 #define	AUDIT_TYPE_NORMAL	1	/* a "normal" audit record */

include/linux/audit_arch.h

···
 	AUDITSC_NVALS /* count */
 };
 
+extern int audit_classify_compat_syscall(int abi, unsigned syscall);
+
 #endif

kernel/audit.h

···
 extern void audit_put_tty(struct tty_struct *tty);
 
 /* audit watch/mark/tree functions */
-#ifdef CONFIG_AUDITSYSCALL
 extern unsigned int audit_serial(void);
+#ifdef CONFIG_AUDITSYSCALL
 extern int auditsc_get_stamp(struct audit_context *ctx,
 			      struct timespec64 *t, unsigned int *serial);