x86: move extern declaration to vdso.h

Before:
   total: 0 errors, 3 warnings, 685 lines checked
After:
   total: 0 errors, 1 warnings, 678 lines checked

No code changed:

arch/x86/kernel/signal_32.o:

   text	   data	    bss	    dec	    hex	filename
   5333	      0	      4	   5337	   14d9	signal_32.o.before
   5333	      0	      4	   5337	   14d9	signal_32.o.after

md5:
   c279e98012a2808e90cfa2a7787e42a4  signal_32.o.before.asm
   c279e98012a2808e90cfa2a7787e42a4  signal_32.o.after.asm
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/signal_32.c

@@ -342,13 +342,6 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size)
 	return (void __user *) sp;
 }
 
-/*
- * These symbols are defined with the addresses in the vsyscall page.
- * See vsyscall-sigreturn.S.
- */
-extern void __user __kernel_sigreturn;
-extern void __user __kernel_rt_sigreturn;
-
 static int
 setup_frame(int sig, struct k_sigaction *ka, sigset_t *set,
 	    struct pt_regs *regs)

include/asm-x86/vdso.h

@@ -25,4 +25,11 @@ extern const char VDSO32_PRELINK[];
 	(void *) (VDSO32_##name - VDSO32_PRELINK + (unsigned long) (base)); })
 #endif
 
+/*
+ * These symbols are defined with the addresses in the vsyscall page.
+ * See vsyscall-sigreturn.S.
+ */
+extern void __user __kernel_sigreturn;
+extern void __user __kernel_rt_sigreturn;
+
 #endif	/* asm-x86/vdso.h */