cr-restore: align the stack on 8-byte boundary

The section 5.2.1.2 of the AAPCS says that the stack must be 8-byte aligned
and this rule is broken when the thread restore_task_with_children()
is forked by the function fork_with_pid() since the variable ca
and its field stack are likely to be 4-byte aligned.

This patch forces 8-byte alingment of the field cr_clone_arg::stack.
This made the following tests pass on ARM:
* static/shm,
* static/ipc_namespace.

Particulary the unaligned stack results in incorrect passing
of the 64-bit argument to the function snprintf() in the function
sysctl_write_u64().
Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -777,7 +777,7 @@ out:
 
 /* All arguments should be above stack, because it grows down */
 struct cr_clone_arg {
-	char stack[PAGE_SIZE];
+	char stack[PAGE_SIZE] __attribute__((aligned (8)));
 	char stack_ptr[0];
 	struct pstree_item *item;
 	unsigned long clone_flags;