x86/unwind/orc: Fix !CONFIG_MODULES build warning

x86/unwind/orc: Fix !CONFIG_MODULES build warning

To fix follwowing warning due to ORC sort moved to build time:

  arch/x86/kernel/unwind_orc.c:210:12: warning: ‘orc_sort_cmp’ defined but not used [-Wunused-function]
  arch/x86/kernel/unwind_orc.c:190:13: warning: ‘orc_sort_swap’ defined but not used [-Wunused-function]

Signed-off-by: Shile Zhang <shile.zhang@linux.alibaba.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/c9c81536-2afc-c8aa-c5f8-c7618ecd4f54@linux.alibaba.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>