x86, kprobes: remove sparse warnings from x86

arch/x86/kernel/kprobes.c:584:16: warning: symbol 'kretprobe_trampoline_holder' was not declared. Should it be static?
arch/x86/kernel/kprobes.c:676:6: warning: symbol 'trampoline_handler' was not declared. Should it be static?

Make them static and add the __used attribute, approach taken from the
arm kprobes implementation.

kretprobe_trampoline_holder uses inline assemly to define the global
symbol kretprobe_trampoline, but nothing ever calls the holder explicitly.

trampoline handler is only called from inline assembly in the same file,
mark it used and static.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Acked-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/kprobes.c

@@ -581,7 +581,7 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
  * When a retprobed function returns, this code saves registers and
  * calls trampoline_handler() runs, which calls the kretprobe's handler.
  */
-void __kprobes kretprobe_trampoline_holder(void)
+static void __used __kprobes kretprobe_trampoline_holder(void)
 {
 	asm volatile (
 			".global kretprobe_trampoline\n"
@@ -673,7 +673,7 @@ void __kprobes kretprobe_trampoline_holder(void)
 /*
  * Called from kretprobe_trampoline
  */
-void * __kprobes trampoline_handler(struct pt_regs *regs)
+static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 {
 	struct kretprobe_instance *ri = NULL;
 	struct hlist_head *head, empty_rp;