sh: Export unwind_stack() to satisfy modular oprofile.

If the oprofile code is built as a module, unwind_stack() as used by the
oprofile backtrace code is not available, causing build breakage.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/kernel/unwinder.c

@@ -11,6 +11,7 @@
 #include <linux/errno.h>
 #include <linux/list.h>
 #include <linux/spinlock.h>
+#include <linux/module.h>
 #include <asm/unwinder.h>
 #include <asm/atomic.h>
 
@@ -160,3 +161,4 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs,
 
 	atomic_dec(&unwinder_running);
 }
+EXPORT_SYMBOL_GPL(unwind_stack);