x86/audit: Fix a -Wmissing-prototypes warning for ia32_classify_syscall()

Lift the prototype of ia32_classify_syscall() into its own header.
Signed-off-by: Benjamin Thiel <b.thiel@posteo.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200516123816.2680-1-b.thiel@posteo.de

arch/x86/ia32/audit.c

 // SPDX-License-Identifier: GPL-2.0
 #include <asm/unistd_32.h>
+#include <asm/audit.h>
 
 unsigned ia32_dir_class[] = {
 #include <asm-generic/audit_dir_write.h>

arch/x86/include/asm/audit.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_AUDIT_H
+#define _ASM_X86_AUDIT_H
+
+int ia32_classify_syscall(unsigned int syscall);
+
+#endif /* _ASM_X86_AUDIT_H */

arch/x86/kernel/audit_64.c

@@ -3,6 +3,7 @@
 #include <linux/types.h>
 #include <linux/audit.h>
 #include <asm/unistd.h>
+#include <asm/audit.h>
 
 static unsigned dir_class[] = {
 #include <asm-generic/audit_dir_write.h>
@@ -41,7 +42,6 @@ int audit_classify_arch(int arch)
 int audit_classify_syscall(int abi, unsigned syscall)
 {
 #ifdef CONFIG_IA32_EMULATION
-	extern int ia32_classify_syscall(unsigned);
 	if (abi == AUDIT_ARCH_I386)
 		return ia32_classify_syscall(syscall);
 #endif