x86: mce.h: Fix warning in header checks

Someone isn't reading their build output: Move the definition
out of the exported header.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: linux-kernel@vger.kernelorg
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/include/asm/mce.h

@@ -108,10 +108,11 @@ struct mce_log {
 #define K8_MCE_THRESHOLD_BANK_5    (MCE_THRESHOLD_BASE + 5 * 9)
 #define K8_MCE_THRESHOLD_DRAM_ECC  (MCE_THRESHOLD_BANK_4 + 0)
 
-extern struct atomic_notifier_head x86_mce_decoder_chain;
 
 #ifdef __KERNEL__
 
+extern struct atomic_notifier_head x86_mce_decoder_chain;
+
 #include <linux/percpu.h>
 #include <linux/init.h>
 #include <asm/atomic.h>