x86: fix irq_lock/unlock ordering bug

Memory accesses could be reordered before an irq_lock() or after an
irq_unlock() without the memory barriers.

See commit 15bc537 for the ARM fix for
a complete description of the issue and fix.

Change-Id: Ic92a6b33f62a938d2252d68eccc55a5fb07c9114
Signed-off-by: Benjamin Walsh <[email protected]>
(cherry picked from commit 1f8125a)

Author: benwrs

include/arch/x86/asm_inline_gcc.h

@@ -82,7 +82,7 @@ static ALWAYS_INLINE void _do_irq_unlock(void)
 {
 	__asm__ volatile (
 		"sti;\n\t"
-		: :
+		: : : "memory"
 		);
 }