x86/i386: Put aligned stack-canary in percpu shared_aligned section

Pack aligned things together into a special section to minimize
padding holes.

Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Tejun Heo <tj@kernel.org>
LKML-Reference: <4AA035C0.9070202@goop.org>
[ queued up in tip:x86/asm because it depends on this commit:
  x86/i386: Make sure stack-protector segment base is cache aligned ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/common.c

@@ -1043,7 +1043,7 @@ DEFINE_PER_CPU(struct orig_ist, orig_ist);
 #else	/* CONFIG_X86_64 */
 
 #ifdef CONFIG_CC_STACKPROTECTOR
-DEFINE_PER_CPU(struct stack_canary, stack_canary) ____cacheline_aligned;
+DEFINE_PER_CPU_ALIGNED(struct stack_canary, stack_canary);
 #endif
 
 /* Make sure %fs and %gs are initialized properly in idle threads */