kernel/sys_ni.c: add dummy sys_ni_syscall() prototype

kernel/sys_ni.c can't #include <linux/syscalls.h> due to cond_syscall(),
but let's tell gcc to not warn with -Wmissing-prototypes.
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sys_ni.c

@@ -4,6 +4,10 @@
 
 #include <asm/unistd.h>
 
+/*  we can't #include <linux/syscalls.h> here,
+    but tell gcc to not warn with -Wmissing-prototypes  */
+asmlinkage long sys_ni_syscall(void);
+
 /*
  * Non-implemented system calls get redirected here.
  */