Wrong unpacked structure for epoll_event on qemu-or1k (openrisc user-space)

[Luca Bonissi]

The or1k epoll_event structure - unlike other architectures - is packed, 
so we need to define it as packed in qemu-user, otherwise it leads to 
infinite loop due to missing file descriptor in the returned data:

--- qemu-20230327/linux-user/syscall_defs.h.orig	2023-03-27 
15:41:42.000000000 +0200
+++ qemu-20230327/linux-user/syscall_defs.h	2023-06-30 
17:29:39.034322213 +0200
@@ -2714,7 +2709,7 @@
 #define FUTEX_CMD_MASK          ~(FUTEX_PRIVATE_FLAG | 
FUTEX_CLOCK_REALTIME)

 #ifdef CONFIG_EPOLL
-#if defined(TARGET_X86_64)
+#if defined(TARGET_X86_64) || defined(TARGET_OPENRISC)
 #define TARGET_EPOLL_PACKED QEMU_PACKED
 #else
 #define TARGET_EPOLL_PACKED