qemu-barrier: Fix compilation on i386 hosts

Commit 1d31fca4 tried to fix bug
introduced by 610b823e by including
qemu-common.h, which breaks the build further.

Include compiler.h instead, as suggested by Blue Swirl.
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

qemu-barrier.h

@@ -6,7 +6,7 @@
 
 #if defined(__i386__)
 
-#include "qemu-common.h"        /* QEMU_GNUC_PREREQ */
+#include "compiler.h"        /* QEMU_GNUC_PREREQ */
 
 /*
  * Because of the strongly ordered x86 storage model, wmb() and rmb() are nops