x86/vdso: Only define prctl_map_vdso() if CONFIG_CHECKPOINT_RESTORE

... otherwise the compiler complains:

  arch/x86/kernel/process_64.c:528:13: warning: ‘prctl_map_vdso’ defined but not used [-Wunused-function]

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: gorcunov@openvz.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: oleg@redhat.com
Cc: xemul@virtuozzo.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/process_64.c

@@ -525,6 +525,7 @@ void set_personality_ia32(bool x32)
 }
 EXPORT_SYMBOL_GPL(set_personality_ia32);
 
+#ifdef CONFIG_CHECKPOINT_RESTORE
 static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
 {
 	int ret;
@@ -535,6 +536,7 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
 
 	return (long)image->size;
 }
+#endif
 
 long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
 {
@@ -590,14 +592,14 @@ long do_arch_prctl(struct task_struct *task, int code, unsigned long addr)
 	}
 
 #ifdef CONFIG_CHECKPOINT_RESTORE
-#ifdef CONFIG_X86_X32
+# ifdef CONFIG_X86_X32
 	case ARCH_MAP_VDSO_X32:
 		return prctl_map_vdso(&vdso_image_x32, addr);
-#endif
-#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
+# endif
+# if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
 	case ARCH_MAP_VDSO_32:
 		return prctl_map_vdso(&vdso_image_32, addr);
-#endif
+# endif
 	case ARCH_MAP_VDSO_64:
 		return prctl_map_vdso(&vdso_image_64, addr);
 #endif